

It depends. The CPU and GPU use the same ram. Increasing the size and swapping to something with higher frequencies and better timings can’t hurt it you are playing games that are stressing the limits of the system. You could give the GPU 10 GB of faster RAM which is what likely holds the system back.
No clue. Don’t even have a steamdeck myself. I’m sure a similar mod could be done if you have the correct ram chips and tools plus the ability to mod the UEFI.