It's your CPU almost certainly, but you can confirm by running a game and checking your CPU metrics on a resource monitor while in casual or something. One thing to test is adding the "-threads [threads_number]" for how many cores you have and see if that helps.

Also check ProtonDB for user performance tricks.

The big reason for CS2 getting laggy from CPU being weak is from the number of threads the game runs to keep the inputs from all the players as live as possible. Increasing the power or number of threads improves the perceived lag you're seeing.

It is the CPU not any operating system. That cpu and platform, it is a bit slow for certain modern games/engines. Especially if its either the first FX generation (8150, etc) or anything under (below) the 8 core ones. The IPC on any ryzen 5000 cpu is almost 3 times more IPC than an FX. Another variable is your GPU is way faster than what the CPU can process and it will bottleneck on any FX platform and might be using 50-75% of what the GPU can deliver. So it might be running like if it was a 6600 or slower even though the GPU is way more powerful. Those CPU make great home servers nowadays.

Guide: https://archive.org/details/manualsbase-id-78410/page/12/mode/2up

If you can't upgrade to something newer you might want to check the FX guide that used to be on the AMD website (provided the link above) that tells you how to overclock the CPU through the NB but don't do it to overclock the CPU but just the NB and then underclock and undervolt everything near or the same as stock. This will make the CPU open up and run way better. Most of the times the NB might come at 2200 if Im not mistaken you can overclock that to 2400.

• You will need to raise the voltage (believe its NB) for that which I forgot the name but is in the guide.
• Be aware some motherboards won't post when you do this if the board has weak VRMs or are cheaper boards. The chipset 990 or 970 has nothing to do with the construction and quality of the motherboard.
• If your ram is 1866mhz you can lower it to 1600mhz then raise the NB until you can see the RAM go up to something close to 1866mhz. If your ram is 1600mhz then lower it to the previous speed in the bios and then raise to get to 1600. Since you have 4 sticks of RAM that stresses the Memory Controller on the CPU a bit so if your motherboard is high end it might let you get to 1866 with 4 sticks and might even let you get to 2133mhz.
• Since you provided no details on what you have I can't speculate much.
• Once you raise the NB everything will go up in the clock. So now you have to lower the cpu clock to the closest stock clock. Same with HT link and other clocks lower them to the nearest to stock.
• Also if you can match the HT with the NB at 2400 that will also make the system spend less power and be smoother.

IF nothing posts when you do this you need to reset your bios through the pins close to the CMOS battery (either using jumper pins or with a metal screwdriver). In that case its best to leave the NB at 2200mhz and lower the HTlink to 2200mhz. Some motherboards if they are higher end it will allow you to go to 2600 in the NB and HT but most wont allow that. Cheaper boards wont allow you to go to 2400mhz and will stay in 2200 you can lower the HT to 2400 or 2200 to make it run less stuttery.

This is all by my experience, but my advice is to read the guide and understand a bit more of what you can do. Don't trust anything I say without reading the AMD guide first and deciding what to do because I haven't worked on the platform in a while and may be mixing the NB and HT. But the one you should raise that I remember is the one that default is at 2200mhz. The other will be at 2600mhz unless the board is not too powerfull both might be at 2200mhz. At least with that as a reference you might be able to squeeze a bit more from that platform.

I apologize I didn't write all of this in an ordered way.

have a gtx 6700 gpu which should be plenty overkill for cs2. But ive heard cs2 is processor heavy.

I don't know which game you're playing, not sure what CS2 is, as some other folks mention. However, if you install mangohud and run it via mangohud <gamename>

if this is Steam, in the game's Launch Options, that'll be "mangohud %command%"

it'll show you CPU and GPU load in an overlay on top of your game.

EDIT: Example:

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EDIT2: Note that by default, it shows "composite CPU load", same as top does by default. So, say you have a 32-core CPU and a game uses only a single thread, then it'll only show it running at 3%, even if the game is bottlenecked on the single core that it's using. MANGOHUD_CONFIG=full mangohud <gamename> will show all CPU cores independently (along with some other data). E.g.:

collapsed inline media

It sounds like you're using Counter-Strike 2 from other comments, and that CS2 only really uses 1-2 cores:

https://steamcommunity.com/app/730/discussions/0/594026537713459453/

CS2 still heavily loads only 1–2 CPU threads, even on modern CPUs with multiple high-performance cores. Other cores remain mostly idle while one thread runs at 100%.

I know I’m about to get rotten fruit thrown at me… but if you’re finding this rig almost good enough and don’t use it for anything security-sensitive, disabling CPU exploit mitigations will get you a substantial boost (~20-30% additional IPC throughput).

Only go this route if you understand the repercussions; see Arch Wiki for details: https://wiki.archlinux.org/title/Improving_performance

Cities skylines 2 is insanely unoptimised and runs terribly on even high end systems. What is your city size?

Might be a bit of both. Any pre-Ryzen CPU is very long in the tooth now and one from 2010 really isn't going to cut it for almost any modern game. But I've also read of many people having Linux-specific issues in CS2.

is it the fault of my 15 year old amd fx cpu, or is it linux? I have a gtx 6700

It's your CPU. If you are up for purchasing new hardware, a Ryzen processor (5000 series or better) will be a massive upgrade and are very prevalent on the used market.

It's your CPU. The FX line came out a very, very long time ago, the first real quad cores. You need an upgrade to play games that came out last year. (Edit, I thought you meant Cities Skylines 2. Still, if you're hoping for good framerates you can't have a CPU that is that old)

I actually had to deal with mouse movements being wonky, where it didn't work at all. I had to use my trackball mouse to even aim. That was stupid of Valve for a Razer mouse.

GTX 670? RX 6700? GeForce 6700 XL? Your GPU doesn't exist dude.