"Heart" actually doesn't function as "remember" as there's no way to see songs in Apple Music (not in your library) that you've previously "loved"[1]. It's supposedly used to help refine recommendations[2].
I could be wrong, but I'm not sure how else they'd be showing up in my library under "Recently Added" then. I didn't specifically create any new playlists or anything and it's just the songs I "hearted".
I assumed it was just a "genius" thing at first as well, but there they are. Maybe it's new.
I assumed it was just a "genius" thing at first as well, but there they are. Maybe it's new.