Maybe I underestimated the problem in the above description because I have been avoiding iTunes for several months. I recently bought a new iPhone 7+ and want to put music on it, and authorize it for testing with xcode, and realize that iTunes is unusable.
I think it started when I upgraded to High Sierra earlier in 2018. THat's when I stopped using iTunes.
Currently, I am using version 10.13.4, and iTunes always opens with error 42110, and then the spinning beach ball for between 30-120 minutes (most often >30 minutes). If I plug in a phone, the error and beach ball re-appear and the whole system becomes unresponsive for hours, or a re-boot, which also can take an hour. CleanMyMac does sometimes give me an option to force quit, which can be a life saver if I need my system to work quickly.
I can also NOT download purchases made on other devices. Even when I see the items that I have purchased (Account --> Family Purchases) I alway get an error message: Could not purchase "Album name". An unknown error occurred (-42032). There was an error in the iTunes Store. Please try again later.
I can also NOT fully syncronize my phone with my iTunes library selections. I don't think an error is shown, it just doesn't work properly - runs through the steps, but only a small number of albums (20% max) are copied across. I have Sync Music selected; and Selected playlists, artists, albums, and genres also selected.
Other common errors: iTunes could not check for an update to the carrier setting for your iPhone. An unknown error occurred (-50).
Is there an alternative way to purchase and manage music across my devices other than iTunes, or are these problems solvable?