There is an emulator like this: GitHub - aweigit/freej2me-miyoomini: freej2me for miyoomini
However, unfortunately, it only works on stock firmware of Anbernic, Miyoo Mini and Trimui Brick. Is it possible to adapt it to MuOS? I tried to make it as an app, but due to lack of knowledge, it didn’t work out.
I tried launching games through RA, but it always works incorrectly: either a white screen, or it doesn’t launch, or it launches with artifacts, or something else. Sometimes it even freezes the console.
Use core from Core Downloader. It works very good. But keep in mind that games must be 320x240. And yes, not all of them work correctly. Not because the core is bad, but because jar files vary greatly in quality. I recommend that you use jar files from dedomil.net and download all available ones for the 320x240 resolution (or 240x320 in some cases). Then try them all, and most likely one of them will work. I repeat, this is not a core or MuOS problem. This is just how the platform is.
I tried this but I got different problems for the same game as described in the post. That’s why I wondered if the emulator from the post could be adapted for MuOS, bypassing RA.