Hi Ted,
While we understand wanting to wait before upgrading to a new operating system, especially if you are using programs you are unsure how they will work with the new software, please note that keeping your Mac up to date ensures you have the most recent security updates available.
We can't speak for ProTools, but we can say that you would add your music from your Mac to the Music app.
Found in the Apple Music User Guide for Mac, the article Import music from a computer to Music on Mac says:
If you have songs or music video files on your computer, you can import them into Music so they appear in your music library.
1. In the Music app 
on your Mac, choose File > Add To Library or File > Import.
If you selected “Copy files to Music Media folder when adding to library” in Files preferences, you see File > Import.
2. Locate a file or folder, then click Open.
If you add a folder, all the files it contains are added to your library.
And Access your music library on all your devices shows the steps for syncing:
1. In the Music app on your Mac, choose Music > Preferences, click General, then select the Sync Library checkbox.
If you don’t see this option, sign in to Apple Music using your Apple ID. You must be an Apple Music subscriber to access your music on your other devices using Sync Library.
2. To turn on your music library on another device, do any of the following:
• Another computer: In the Music app on your Mac, sign in to the iTunes Store using the same Apple ID that you used on the first computer, then choose Music > Preferences, click General, then select the Sync Library checkbox.
•An iPhone, iPad, or iPod touch: On your device’s Home screen, tap Settings, tap Music, then tap to turn on Sync Library.
To find out how to add music to your device and listen offline, see the user guide for iPhone, iPad, or iPod touch. If a device doesn’t have the latest version of iOS or iPadOS, get the user guide from the Apple Support Manuals website.
Use Pro Tools - Music Creation Software - Learn and Support for questions regarding upgrading how the program will work with the new OS's in your Apple devices.
The above information should help answer your questions on how to import your music into the Music app.
Have a great day!
