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#21
This is what your system volume information folder should look like with no restore points:
I think you can go ahead and delete SystemRestore/AppxStaging. You can do this however you like - boot from external OS, recovery environment, install USB, Linux as you wish - any will give you authority. You could try even taking authority but this would be more complicated.
There might be some table containing links and system restore might break but if you don't want to clean install yet then try it. Then turn on system protection, create a restore point and restore to it. That will prove if it works or not.
I think your problem is due to this System Restore fails: AppxStaging %ProgramFiles%\WindowsApp 0x80070091 - Windows 10 Forums which is fixed now apparently.
There might be some table containing links and system restore might break but if you don't want to clean install yet then try it - you have nothing to lose. Then turn on system protection, create a restore point and restore to it. That will prove if it works or not.
If it doesn't work you don't lose anything - Windows will keep on working - just not system restore.