Topic on Talk:Atomic Heart
There's now a QoL Tweaks mod which should be able to set this cvar for you automatically: nexusmods.com/atomicheart/mods/22
Was about to add a section to main article but noticed some users did report certain anims were breaking with that unfortunately... I played for a while using cvar change and never noticed any broken anims with that though, so not sure if it's an issue with how that mod works, or maybe certain setups just don't work well with TargetFPS stuff being changed.