There's plenty of "relatively compact" ARM-based handhelds targeting the retro market already, but many of them are shipping with a pitiful amount of RAM (1GB or so) making them an absolute non-starter, while others (selling for significantly higher prices) run crappy Android-based OS's that will never be updated. There is a gap in the market for a good-quality retro-like handheld shipping with a Linux-native OS (or even just enabling one to be installed trivially after-the-fact, with everything working and no reliance on downstream hacked-together support packages).

Retroid Pocket 5 supports Android and Linux dual boot.