So I learned that the CSGO FPS drops are a real issue, but apparently only limited to a small player base, so I guess it may be hardware related? This is a typical response, that not everyone is impacted.
Anyway, Valve released a new patch today, but didn't address the FPS issue, so... it could also be driver related then, I can't see Valve ignore this.
EDIT: It seems Valve has messing about making the game more compatible with Linux, and today's patch apparently broke the game on Linux... Don't know, I don't use Linux, but them optimising controllers means that they want this game on the Steam Deck, eeuw. I wouldn't be surprised that it is these 'optimisations' which has broken the game.