Hello,
I own a Miiyo mini plus, rg nano and an powkiddy rg30.
Is it possibly to use my official pico8 license on that devices?
Or is that not possible because that devices are not windows/linux based?

As I see, retro game consoles generally are based on Linux system. You can run some Linux exports on them.

But this might require some adaptation work on your part if the developer of the console didn't do this.

«linux» is not a very precise descriptor, it’s like saying «computer» :)

some of these emulation handhelds use ARM CPUs that are compatible with the raspbian build of pico-8. you have to pick the right version (32 or 64-bit) and try each of the pico8 executable (static or dynamic link)! there are a number of threads here of people having success on their device. if you have a powkiddy rgb30 (your post is missing the «b»), then it’s perfect for pico-8 and there are many guides around for the configuration!