Hi groovedane,
Since the scroll bar in Apple Music keeps disappearing on your Mac, it would be a good idea to check to see if the issue persists in safe mode.
You can do this by checking out the link below.
Start up your Mac in safe mode
Before you begin
To start up your Mac in safe mode, you need to know what type of Mac you have.
1) On your Mac, choose Apple menu > About This Mac.
2) Look at the information in the window to determine what type of Mac you have:
*If you see an item labeled Chip, followed by the name of the chip, you have a Mac with Apple silicon.
*If you see an item labeled Processor, followed by the name of an Intel processor, you have an Intel-based Mac.
Use the corresponding set of instructions below to start up your Mac in safe mode.
Start up your Mac with Apple silicon in safe mode
) On your Mac, choose Apple menu > Shut Down.
Wait for your Mac to shut down completely. A Mac is completely shut down when the screen is black and any lights (including in the Touch Bar) are off.
2) Press and hold the power button on your Mac until “Loading startup options” appears.
3) Select a volume.
4) Press and hold the Shift key, then click Continue in Safe Mode.
The computer restarts automatically. When the login window appears, you should see “Safe Boot” in the menu bar.
Start up your Intel-based Mac in safe mode
1) Turn on or restart your Mac, then immediately press and hold the Shift key until you see the login window.
2) Log in to your Mac.
3) You might be asked to log in again.
On either the first or second login window, you should see “Safe Boot” in the menu bar.
Verify your Mac started up in safe mode
If you’re unsure whether your Mac started up in safe mode, you can use the System Information app to check the mode.
1) On your Mac, press and hold the Option key, then choose Apple menu > System Information.
2) In the System Information app, select Software in the sidebar.
3) In the System Software Overview, look at the value listed next to the item labeled Boot Mode.
*Safe: The Mac is using safe mode.
*Normal: The Mac is not using safe mode.
Performing this step above may help resolve the issue or allow us to isolate the problem further.
If you're still experiencing the same issue, then try testing in a new user to see if you're still noticing the same problem there: Change Users & Groups settings on Mac
Please let us know the outcome after giving the above steps a try.
Thanks for using the Apple Support Communities.
Cheers!