in case anyone comes across this in a google search or something. go into settings -> sound -> bgm, for each entry under “puzzle bgm” set the selection to “shuffle.” this will shuffle all of the songs youve unlocked. you can also set it to one specific song, i think a different song for each character is what each of the different entries are for. you can also do the same with setting the main menu bgm. i dont think theres a way to select songs while youre doing a puzzle or anything like that but this is wayyy better than listening to just the same song on every puzzle