Personal CD collections scanned into Music app. Cant seem to sync / add to my new iPhone 15Pro

Ive spent many many years scanning my personal CD collection into the old iTunes Library (now Music). In more recent years, additional music I've bought through Apple Music store have been added to the library too as I've moved away from physical CD's (although I still do buy physicals at times).

I don't like using the "Sync Library" option in Music, because I tried it once and quite a lot of my personal music never properly uploaded to this Apple service (ie albums and some songs on some albums were not uploaded or would not be played back and the artwork for many of the albums was scrambled from their originals - I had spent years carefully curating my personal library and suddenly it was no longer complete and with artwork from the wrong albums.

There has never been a problem in the past with syncing my entire curated music library onto my iPhone / iPods etc. Until I just upgraded to the new iPhone 15Pro. I cannot find where it will allow me to sync from my Music library on my Mac, as I always have without using the Apple Cloud service (which doesn't work perfectly). Can anyone assist? I feel I have made a grave mistake upgrading to the latest iPhone product. My music collection has been a lifelong project and means the world to me and suddenly I seem to only be able to stream or load music I have purchased through the Music app. - and locked out of my personal library.

Thankyou in advance for any or suggestions.