You have to change your es_systems.cfg in your “/userdata/system/configs/emulationstation” folder search in the file for “Sega32x” and change the <group>megadrive</group>
tag to <group>sega32x</group>
If your es_systems.cfg is not located in the mentiond path than copy it from “/usr/share/emulationstation/” to the folder I named.
Worked for me in Batocera v34