You can make smart playlists- but you might have to do that on the Mac. Smart playlists collect songs by whatever criteria you want- say music you hearted from the 90s added in the last 6 months. You can go wild with custom selectors and they’re live updating. Those lists get synced to all your devices. Playlists can be nested in folders- again you might have to do that on the Mac side. I’m not sure in iOS you can move contents of folders or lists into each other but on the Mac it’s drag’n’drop. I do wish iOS music app had a mechanism for creating and adjusting the smart lists though, because they’re great.