@rgbfr

What do you think the problem is?

It could be the ROM, it could be the ROMSET/file format, it could be the videomode....
Check these possibilities.

https://wiki.recalbox.com/en/tutorials/games/generalities/isos-and-roms/romsets-for-recalbox https://wiki.recalbox.com/en/tutorials/video/display-configuration/complete-video-configuration-guide https://forum.recalbox.com/topic/25635/recalbox-8-0-dreamcast-problème-chd-v5