The problem seems to be Music. My music have transferred from iTunes on my old iMac to Music on my newer iMac. But the Playlists I had in iTunes were not transferred. This is previoulsly purchased and all my cd's imported into iTunes.
I have theese playlists in Music on my iPhone so I thought no worries. With iTunes there was never any problems syncing between phones or between computers or between phone and computer. But with Music I can only transfer what is in Music on iMac to the phone which will erase every playlist on my phone. I can not, simply, transfer the playlists in Music on my iPhone to Music on my iMac. No way ! Why ?
I have tried with the sharing thing also (family sharing or what it is called) - which I used to transfer my musik cd's from an old Mac laptop with dvd/cd drive to iTunes on iMac with no dvd/cd drive and then onto phone. This option is not working either.
I have some mp3 files sitting on my desktop that I want on my iPhone to listen to. No way in **** is that going to happen unless I put them in Music on iMac and sync the phone and then loose my Playlists on the phone.
Apple has fixed something that worked for me into something that I am giving up on. I will do as my daughter and my workplace and change to Androids if this doesn't get better.