You likely need to fix the borked gaming service via some Powershell commands as described here:
After you’ve done that it will still take a while until the update propagates to the now repaired Store app. Since I’ve done that it worked via the “Get Updates” menu entry exactly ONCE, now I always have to click the “Flight Simulator Premium Deluxe” entry in the “Installed” category so the product page opens, only there I’ll find the “Update” entry when clicking the 3 dots button.
That’s not correct. It’s still supposed to work without that app, installing the Xbox app is just a simple workaround to get around the borked gaming services issue. Doesn’t always work tho.