hey! so i had the exact same problem here, i knoe this question was from awhile ago but if anyone else has this problem now maybe try this. i am using my old iphone 6😀 for my music because trust me i have a lot and my phone now can’t hold all the storage it takes up (like 27 gb) anyways i recently signed into icloud and everything onto the phone, deleted everything but apple music and i went to look at why my songs weren’t downloading system storable was taking up ALL my storage, wtf, i deleted everything how could this be possible, i searched for an answer nothing worked, and so i was like, well let’s sign out of icloud f it let’s see, and magically it took away all the system storage, so try restarting phone if that doesn’t work, sign out of icloud and sign back in, i never signed back in because i’m just using the phone for music but. hope this helps