Depends

https://steamdeck.com/en/verified

All these game will work swimmingly. Those marked playable will usually work perfectly fine out of the box, but maybe have an ugly launcher or something you need to use the touchscreen for. Those marked unplayable will have bugs but in my experience work fine too. There's a more detailed less conservative compatibility db online too.

In terms of power it's about between a PS4 and PS4 Pro, with a faster CPU, more RAM, slower GPU, but with a really fast NVMe SSD so games like CP2077 are very playable but not at the highest settings.

Gotta remember the Deck has a 7.4" 800p screen, so its not comparable to the horse power needed for a PC at 4K or something.

Most consoles end up around the same render res once you've accounted for checkerboarding, dynamic res and DLSS/FSR nonsense.

The deck also does shader pre-compilation and caching for games on steam so it often performs much better compared to a Windows PC with the same hardware for example.

Anything ray tracing is out of the question though as it uses AMD, not Nvidia.

I don't play AAA games (nor know what new ones are there) - if you have a game in mind I could try it and report back?

The only game I tried that it really struggled with was NFS Unbound.

I was also able to do PS3 emulation on it, including Skate 3 and Motorstorm.

I can play zero dawn on mine and boy did it make train rides tolerable.

What LainTrain said. But you might find yourself playing less powerful games - emulators, Factorio, Hades, stardew, modded mc, etc...