I don't understand, Retroarch on Miyoo Mini prefectly saves states. I know that for a fact since I recently finished Chrono Trigger on it.

I have Miyoo Mini and it's great. Community is very helpful, and OnionOS is simply awesome. But it's really small, and my hands cramp if I play a bit longer. Also, any game that requires shoulder buttons frequently is pretty much unplayable without remapping, also due to the ergonomy. I am thinking about getting a 3D printed holder for it...

The best Tetris implementation, IMHO.