Hey Frederic,
I would be happy to restore some of the older themes. I will go through and convert some of them for the new theme format. In the meantime you can manually convert them using this tool: https://minimeters.app/theme_converter/
Depending on your OS the older themes should be moved to %AppData%\MiniMeters\v08x_backup on Windows, or ~/Library/Preferences/MiniMeters/v08x_backup.