Hi Long,
Given what you tested, I would stop chasing the Store path. Since Win+A still opens Quick Settings, the shell is at least partly working, and because the issue happens in a new admin account too, it is unlikely to be just one corrupted user profile. Quick Settings is where the volume control lives, and Win+Ctrl+V opens the sound output page in Quick Settings.
Try these next, in this order:
Clean boot the machine and test the speaker icon again. A clean boot starts Windows with only essential drivers and startup programs, which helps isolate background software conflicts.
If the icon works in clean boot, something non-Microsoft is interfering. Re-enable startup items/services in batches until the culprit shows up. Microsoft’s clean boot guidance is designed for exactly that kind of isolation.
If this started after a recent update, remove the latest quality update from Windows RE or from Update history. Microsoft says recently installed updates can be uninstalled, and Windows RE includes an Uninstall Updates option.
For a workaround that avoids the tray icon entirely, use Win+Ctrl+V or open Settings -> System -> Sound -> Volume mixer and control volume there. Microsoft documents both paths.
One practical next test: boot once in Safe Mode or do a clean boot. If the speaker icon works there, the problem is almost certainly a third-party startup item, driver, or shell hook rather than Windows itself. Microsoft’s clean boot guidance is the best official way to prove that.