I gifted a Brick Hammer[1] to my brother-in-law for Christmas. It's an amazing little device, form factor of a Gameboy Pocket and can run games from the PS1/N64 down to NES. The build quality is extremely high too (I got him the metal chassis version). I think it can even run 3DS games, but don't quote me on that.
[1]: https://retrohandhelds.gg/trimui-brick-hammer-review/ (most links are to third-party resellers, so a link to a review is probably safest)
Thanks, but same problem. I meant "NES" as a stand-in for "retro games".
Now, what I would almost certainly buy is a Steam Deck in that size. It doesn't need to be as powerful as a Steam Deck (impossible, of course), just enough to play 2D indie games.