Hi and thanks for this game.
For whoever can't start it onLinux, try run game executable (./moonday-linux/Moonday) in the installation dir. via terminal and check all debug messages.
In my case it tells me libSDL_mixer-1.2.so.0 library is missing so I need to install a proprer package (on Ubuntu 18.04 and its derivates it would belibsdl-mixer1.2 package) and now game starts correctly.

Thanks.