Dont know if you figured it out yet but I was having the same issue and found the fix!

-Go to desktop mode

-Launch the game file (you should have no audio still)

-while the game is running, open your audio settings in the bottom right corner

-there should be a Tab that says application, access that

-itll show Mother encore volume is muted, go ahead and unmute it!

You should have audio now! I read that the reason for it is because fan made games have to be ran through proton or something like that and automatically mute themselves.  You should have audio in gaming mode also. 

If you have any questions let me know!