A couple of ideas for you.
- Earlier on, when I first wanted to install the Standard version, nothing I could do worked. I used up megabytes of data transmission, but couldn't get the whole thing downloaded. Nothing worked. Then someone said "try using a VPN", which I did - and it worked!
- Recently, with SU 5 (an update), I couldn't download it from the MS Store, and there is now no other way to download updates other than through the store. If I logged in to the sim, it would log me out again, and send me to the store. When I got to the sim, it told me everything was OK and go back to the sim. It was a genuine endless loop! Again, someone said "the trick is to install the Xbox app, and if it is installed, shut it down and restart it." Again, not very confident of this solution, but indeed - it worked.
- Yes, this is the Microsoft support site, but it isn't the Microsoft Flight Simulator support site. That's at https://www.flightsimulator.com/. If you go there, you will find lots of FAQs about this stuff, plus a zendesk to log problems. If this doesn't work for you, head in to the forums, register yourself, and look for answers, ask questions there. You'll find a wealth of information there on many topics MSFS. Once you're up and running,
https://flightsim.to/ is a great site for lots of addons to improve your experience - all free, too.
Let us know how you get on with this, and whether any of the suggestions have been of any help.
Good luck
John Glossop