Just thought I'd give you an update - I eventually took a deep breath, backed up the user's files and downgraded the operating system to Windows 10. I'd already tried all the options in both zoom and Windows Sound, and updated the audio driver directly from the manufacturer, and none of these was able to fix the issue.
Now I can hear music!
I'd only recommend downgrading as a last resort - it's pretty much a "wipe everything and re-install from scratch" operation. The windows installer won't let you keep apps and files - everything is wiped. So back up those files, and make sure you have all your logins copied, too. You'll need to re-download and re-install all your programs.
My conclusion - either Zoom isn't properly instructing Windows 11 to turn off the suppression, or Windows 11 is ignoring Zoom's options. This laptop came with Windows 11, and downgrading to Win 10 wasn't a step I took lightly.