Have you gone through this procedure?
“Are you running Windows S mode? This is a locked down version of Windows which will require switching ‘out’ of S mode via the Microsoft App Store.
If not:
You can check whether your pc is set to download apps from outside the MS store.
Settings>Apps>Apps and Features>right at the top of the screen, you’ll see a drop-down menu under Installing apps. There are three choices: Allow apps from anywhere, warn me before installing apps from outside the Store, and Allow apps from the Store only. Choose the option you want (in your case you’ll need allow apps from anywhere or warn me) and close the Settings app. Your changes are saved automatically.”
Seriously, I couldn't figure out what changed. But that fixed it. thanx