I haven't used iTunes Music / Apple Music for quite some time.
I use third party apps to listen to music which are stored offline within those apps. See my list of various offline apps here.
A good app to listen to your own mp3 files via Dropbox/Google Drive and download them to your local iDevice is CloudBeats Pro. There are also various other apps out there that offer this option but please keep in mind that the music will only be accessible via that third party app not the Apple Music app.
I use third party apps to listen to music which are stored offline within those apps. See my list of various offline apps here.
A good app to listen to your own mp3 files via Dropbox/Google Drive and download them to your local iDevice is CloudBeats Pro. There are also various other apps out there that offer this option but please keep in mind that the music will only be accessible via that third party app not the Apple Music app.