How many levels are there and what are the grid sizes?

This game has some amazing music, but I can't find the OST anywhere. Does anyone have any luck finding the music for this game?

I'm trying to play the game on steam deck, but I can't even get past the starting screen where they ask for quality settings etc. because none of the controls nor the touch screen responds. Does anyone know if the game is actually playable on steam deck?

Coming from other titles where the numbers don't gray out until you've actually blocked them in with X's, it's incredibly disorienting that the game grays out things that are complete but open-ended. I can finish a line horizontally that completes bits of vertical, and because I don't realize they're actually complete, I misread what numbers are left entirely. On top of that, the game is routinely spotting you with completions you shouldn't know about. Defeats the point of doing picross if the game's gonn...

I just finished some side quests and got the blessing and curse of the mermaids. What do they do? I found no description anywhere.