Please understand that whenever opening a issue and assistance topic you always need to provide your garuda-inxi regardless of weather you think it's needed or not.
Do check if using various options provided on protondb for CS:GO for PC players. The page starts with comments from steam deck users if you scroll down you will notice the PC section as well.
Also try the various performace tweaks in garuda assistant
For me on a laptop with nvidia gpu and plugged to wall to enable performance mode and turbo boost I use the following steam launch options to get a good experience.
mangohud prime-run %command% -novid -console -high -nojoy -fullscreen +fps_max 0 +cl_forcepreload 1 -tickrate 128 -freq 60 -noborder -threads 4 +mat_queue_mode 2 +mat_disable_fancy_blending 1 -limitvsconst -forcenovsync +r_dynamic 0 -disable_d3d9ex -r_emulate_g -softparticlesdefaultoff
you can completely ignore the mangohud and prime-run commands they are needed for me to offload the game to my dedicated nvidia-gpu and attach the mangohud overlay as you might already know.
The value after -freq corresponds to my monitor's supported frequency which is 60Hz
the value after -threads corresponds to the number of physical cores my CPU has. Some ppl give this option the number of logical threads your CPU supports but for me this exact option with this exact value is needed to launch the game.
So you can take your time playing around with the options and adding/removing what you feel until you reach a system that works for you.