I'm trying to transfer music to my Apple iPhone 11 Pro

I recently bought some music from Apple to have it on my telephone and then to use in my car through Bluetooth. I already have a good selection on the phone but I wanted these as an addition and I put them in a seperate file called New Music September 24

I'm using a iMac from 2017 - and macOS Ventura 13.6.9. and I'm trying to transfer them to my Apple iPhone 11 Pro

On my old computer everything would synchronise perfectly, but this time I cannot find the right way to synchronise them all.

I have also saved some music from YouTube, that I would like to add to this file, but this is a secondry problem, but any information you have handy on this might help

TIA

[Re-Titled by Moderator]