Same issue here since updating from MacOS Sequoia to Tahoe 26.1. I've tried deleting the Apple Music app's cache, and hope the volume equality will improve as a new cache is built, but so far I'm still encountering the volume differences…
1. Close the Apple Music app completely. Either right-click the application in the Dock and select Quit, or while in Music, select Music then Quit Music in the Menu Bar.
2. Open Finder, select Go then Go to Folder in the Menu Bar.
3. Enter the cache path ~/Library/Caches/ into the text box then click Go.
4. Find the Music Cache by opening the folder starting with com.apple.music.
5. Select the contents of the folder and move them to the Mac's Trash.
6. Empty the Trash by right-clicking the Trash icon in the dock followed by Empty Trash.
7. Restart your Mac.