Ok.
There's no way in the Apple ecosystem to do what you want.
There used to be apps that ran on Macs that were sort of File Managers that could use to to see the file structure of iphones (when connected via USB) and could do what you want to do in terms of copying and moving music files. I used one for something (can't remember) but it was more than ten years ago. I don't know if such apps exist any more or even if such access is possible any more. MacOS and iOS security have changes so much since I used one that it might not be possible any more.
Your best bet is, as I posted yesterday before this thread got out of hand (apologies for my part in that) to search google for music transfer, iPhone file manager, etc. If you find something it will almost certainly not be in the app store. It will be a web download of an app that runs on your Mac which will claim to give you access to your phone's file structure and allow you to copy, move and delete files from your phone to you Mac. Some of them might even do that. They will almost certainly want money before they let you transfer more than a few files across.
You need to be very careful. Do lots of research**. In terms of risk, the best case is that you permanently brick your phone and lose your music for ever. Worst case is worse. Create a new user on your Mac to run it and don't log in to your Apple ID. If in any doubt - don't.
Best of luck.
**search these boards for posts by turingtest2 would be a great place to start your research. No one around here knows more about iTunes/Music than they do.