No, there is a limit to how many songs you can have and BMW will do feck all to change it (they’ll pay lip service to it, but nothing more, you’ll probably need to buy the 2024 model for that).
I think it’s something in your settings that is preventing the sharing of information between the bike and iTunes, or possibly Spotify is set as your default player? I had to ask Siri to play something, it’s the only way of changing the default player apparently.
Make sure you only have a couple of small playlists on iTunes when testing, that way you will know it’s not a ‘file size’ issue.
It does work with iTunes, so it can only be the default player or a lack of permission stopping it from working (unless you have lots of music downloaded on iTunes). I would also ensure that you are only trying to play downloaded music and not cloud based, it’ll be easier to make sure that you aren’t trying to access too many songs