@kamil Sorry, but I must say that you sound a bit arrogant to a team that does a totally free job.
Whenever you need help, be free to open a topic, but try to be kinder, and try to make as much information as possible clear, we can not guess what is happening, you have to say as much information as possible, so that some user or developer can try to help.
- First: Recalbox 6.0 (Codename: Dragonblaze) is no longer an RC, it is a stable version.
- Second: the internal Scrapper was experiencing a lot of problems, so it was temporarily removed, there are several topics in the forum mentioning this. Use an external Scrapper, I recommend ARRM, but you can use the Skrapper, or any other:
https://forum.recalbox.com/topic/11850/arrm-another-recalbox-roms-manager
https://forum.recalbox.com/topic/13953/soft-skraper - Third: you need to convert your mp3 to ogg, with the right specifications, read the WIKI:
https://github.com/recalbox/recalbox-os/wiki/Add-Custom-Music-to-EmulationStation-(EN) - Fourth: MATTEL INTELLIVISION need BIOS, do you have the correct BIOS?
https://github.com/recalbox/recalbox-os/wiki/Add-system-bios-(EN)
NOTE: The easiest way to check if your BIOS is recognized is by Recalbox Manager. BIOS is case sensitive (including extensions), and MD5 must be identical to the one requested. (Recalbox Manager does all this checking, sometimes you have the wrong name, and just rename, sometimes you have the right name and MD5 wrong ...)