One thing I can tell you is that a factory reset will not revert you to Android 9. All it does is erase the user storage, i.e. any apps you installed, any update to pre-installed apps, and all of your settings and data (including photographs, messages, etc). It does nothing at all to the system partition, so will not undo any system updates. The fact is that when your phone receives an update that overwrites the previous system, so it doesn't actually have a copy of Android 9 any more that it could revert to.

Of course a reset is still a hassle: you need to back up anything you want to keep, and you need to set the phone up again afterwards. But you don't need to worry about undoing system updates.

I don't know this device, and don't have any real suggestions for fixing it. You could try booting into Safe Mode and see whether that helps: Safe Mode disables all user-installed apps, so if the card works in that mode it would suggest that one of your apps is the problem. You could try going into recovery mode and clearing the system cache (if you have that option: newer phones tend not to). I assume you have already rebooted the phone a few times.