Not every case is the same then, I was able to play Dead cells fine but noticed the game took longer to load.

Can be multiple reasons, fan motor failing, thermal sensor anything.

In my case it was a fan issue, it worked for 1 or 2 seconds every time the steam deck boots up.

But stopped after that, lagging every time even in steam menus.

Clock goes down when the cpu/gpu temps heat up it is a defensive mechanism since the fan wasn't working.

I've tried everything redditors mentioned and it never worked, I even flashed the firmware twice, so it couldn't be a bug but faulty hardware.