I know you tried reinstalling TF2 already but it's worth trying a completely fresh install first. Remove all the game's files from the install folder, uninstall it from steam and make sure you disable cloud saves for it. Install it afterwards and see if anything changes.

If that doesn't work, backing up important files and reinstalling windows should fix it. You can test this before you do it by installing windows on another drive without formatting anything. It should allow you to dual boot. Boot into the fresh install, get only the drivers you need, install Steam and TF2 and see if anything changes. If it does, good, backup your important files and install windows again, this time formatting the drives with the other windows installs.

I can't give you any advice myself but the people in mastercom's discord have been immensely helpful with fixing issues I've had in the past. You can find the link to it from the main mastercom's website.

Did you change anything in your windows theme or general settings?
I had the issue that I changed my windows theme to something which changes the desktop background every 1 minute and during that change my fps dropped to 0...
may be a cause that something windows sided fucks with your game...

Try doing a full reset of TF2 first. If that doesn't work then either your OS or hardware is causing the issue.

Switch away from closed-source/proprietary programs as they are known to be slower and less efficient than Free and Open Source programs (FOSS). Examples of them are Google Chrome, Adobe Photoshop, and Windows 10.

If you're stuck on Windows 10, then try a Windows 10 privacy tool (like W10Privacy). Look out for any indicators that the creators of those programs are cooperating with Microsoft in some way.

Backup everything important on your computer and reinstall your OS. If you're using Windows 10 then I recommend just installing a Linux Distribution instead because those are 1000x better than Windows will ever be (here's a questionaire if you're unsure of which distro to use). After the reinstallation and optimizations if you still have input lag issues, then it is certainly your hardware.

Update:
I uninstalled TF2 and Steam with ALL the files that come with both, Sys-restored back to 8 days ago (even farther) and then did a factory reset of all of my AMD settings and basically reinstalled new batches of all the AMD stuff and used my personal config files again.. I'm getting performance drops still, But nowhere as bad as it was at the start of the post.. I get at lowest 50 FPS in big fights, 70-90ish in slightly populated areas and about 190+ in empty areas of the map.. I'm currently running master-config.. It's def playable but the game still feels really off, I only have about 40 fps above dropping below 60fps in most huge fight areas.. Which still feels kinda ridiculous for my specs but i guess i can't complain about it improving.. I also attempted to reach-out to the master-config discord cause they're probably gurus with this stuff but unfortunately you need a phone-number linked to your discord to join which i'm not really cool with sadly.. I guess this is the end of the post but if anyone else has any genuine tips feel free to let me know.. Maybe im just spoiled but i might reset windows entirely just to see if i can get back to a steady 250-300 fps no matter what like im use to.

I take it you disabled everything possible in the radeon drivers? I'm pretty sure I had awful problems with those drivers, especially with ReLive and Radeon Chill.

also never had fps problems in tf2 but now if i play tf2 for 20+ minutes my game starts freezing every 30 seconds or so and its nearly unplayable. reinstalled tf2 and reinstalled all drivers on my computer but i cant find the fix and honestly i think i am just going to take a break from game for a while.

Uh.. I'm not really sure what you mean.. Disable everything as in the settings? or like literally disabling the drivers.. I think if i literally disabled the drivers i risk my monitor not working and i obviously wouldn't get any performance at all on the default windows ones.. As far as the settings go i checked them i don't have radeon chill on or anything.. Just minor things like enhanced sync (cause it's nice), I obviously have AMD freesync enabled, Image sharpening that's about it though.. Nothing that would really effect FPS like chill would.. In all honesty i'm thinking about restoring windows completely back to a fresh start it's a pain but it's what id do for my hat simulator game

https://i.imgur.com/PorpznW.png

He really means to disable the options in your Radeon drivers *and* the drivers themselves (I really think you should just uninstall the Radeon drivers), and also to uninstall Radeon software. Don't worry though; your computer will function fine as long as you don't disable drivers vital to the OS (like CPU or Storage drivers). If you uninstall any vital drivers, Window will just replace them with stock drivers. This procedure is just meant to check if the drivers are causing the problem. If they are then you can either install a previous version or if there is an update available, then update your drivers (through the manufacturer site, NOT Windows Update as it is too unreliable when getting driver updates).

Hardware throttling maybe? Check the temps on your CPU and GPU when you play. Check your windows "power saving" settings to make sure it's on active and not passive cooling. Check if you changed something in your fan curves in BIOS.

Either that or you have a virus or bitcoin miner IMO. Or some bloatware running on startup (a game anticheat or similar)

I fixed my issue entirely:
I managed to COMPLETELY fix my issue and now run the game (with master-config comp quality) at about 500-600fps which is more than i could've imagined.. What i did is i had a backup of Windows 10 setup with my apps and settings exactly the way i wanted it on a external HDD i made 2 months ago using the "Create a system image" tool in Windows 10.. And i just system-restored back to that as a final ditch effort before deciding to COMPLETELY reset windows and start from scratch entirely.. I was set back 2 months sure but it wasn't much lost just minor updates had to reinstall like 2 programs or so on.. I was surprised to find out that none of the AMD Driver updates or any of the software updates or anything like that we're the cause of my issues.. It was literally just a windows issue.. Windows randomly decided to start effecting my TF2 experience for absolutely no reason at all it was beyond my control who knows why.. Anyways for anyone who comes across this thread and suffers from HUGE performance drops like me this is what i recommend to you after messing with this for over a week this is my final conclusion:

My fix for TF2 performance issues:
1. Update your drivers make sure it's not a driver issue or any other misc issues
2. Try a TF2 FPS config just for testing if your FPS doesn't improve with a config at all just assume that your Windows has randomly stopped making your TF2 performance work
3. Reset windows entirely, Not system restore back to some other point (this will take your files and settings with it which will in return also make TF2 not work still)
4. Buy a external HDD and use the "Create a system image" tool in Windows 10 to make a backup of your OS after you get it setup and confirm TF2 is working on it so you always have this HDD to fall back on in the event TF2 breaks randomly, You just reinstall the OS from the External HDD
5. Bonus points if you "Create a recovery drive" in Windows 10 it could potentially be helpful lets say TF2 stops working you're reinstalling your OS from your external HDD, This USB could repair any potential boot problems or other issues you run into.. Although this is not necessary to have

Conclusion:
Anyways this is what worked for me.. If you went through all of this and it still doesn't work for you i genuinely could only assume it's a hardware issue.. All my experimenting lead me to believe it's windows fault.. If anyone has any questions click my profile and add me personally and I'll do my best to guide you through it all after spending almost entire days for over a week beating my head against the wall i really hope my suffering will help people in the future good luck!

Do you know what Windows version you have now vs. what you had before?

Just another reason why you should just use Linux (which is soooooooooooooooooo much better) instead of Windows/MacOS.

realize you are on the direct path to becoming a neckbearded mid 20 yr old with no job smugly running arch linux on his ancient laptop

Wow didn't expect to hear from you, But yeah i was using the same version of windows for both apparently.. Which is Microsoft Windows 10 Home or "10.0.19042 Build 19042" It wasn't the drivers or windows updates for either OS so i'm either assuming it was Windows or potentially a source-engine/valve issue.. Either way i'm not surprised valve abandoned the game and windows is windows so.. Both OSes had almost no major differences other than one being 2 months older and the other one randomly deciding to effect performance.. Even in terms of software and drivers on them there almost exactly the same.. I can't really think of any reasonable explanation for the technicality of this other than swapping the OS

https://i.imgur.com/iZQ2LHj.png

I'd just like to interject for a moment. What you’re referring to as Linux, is in fact, GNU/Linux, or as I’ve recently taken to calling it, GNU plus Linux. Linux is not an operating system unto itself, but rather another free component of a fully functioning GNU system made useful by the GNU corelibs, shell utilities and vital system components comprising a full OS as defined by POSIX.

Many computer users run a modified version of the GNU system every day, without realizing it. Through a peculiar turn of events, the version of GNU which is widely used today is often called “Linux”, and many of its users are not aware that it is basically the GNU system, developed by the GNU Project. There really is a Linux, and these people are using it, but it is just a part of the system they use.

Linux is the kernel: the program in the system that allocates the machine’s resources to the other programs that you run. The kernel is an essential part of an operating system, but useless by itself; it can only function in the context of a complete operating system. Linux is normally used in combination with the GNU operating system: the whole system is basically GNU with Linux added, or GNU/Linux. All the so-called “Linux” distributions are really distributions of GNU/Linux.

I learned this fact at some point, but I forgot about this until you mentioned it. Anyway yeah the correct name is GNU/Linux.