I had the very same problem trying to get WU6, nothing helped. However I didn’t delete the sim as that seldomly serves any sense.
I had to remove the gaming services from my registry after finding this on the internet a couple of months ago for anoither problem:
Open Registry Editor
Go to HKEY_LOCAL_MACHINE → SYSTEM → CurrentControlSet → Services
Remove the GamingServices and GamingServices.Net
Restart Computer
Go to your Windows Store → 3-dot-menu → Downloads and Updates → Check updates
Gaming Services should install now without issue.
Double check by rebooting and going back to Windows Store and trying to Get Updates again - you should be Up to date
At that point I could NOT reinstall the gaming services, which indicated that there was a more serious issue with the store which also affected my ability to update MSFS. So I deleted the MS store cache and resetted it, instructions are easily searchable.
Then I did this which forces a redownload of the gaming services:
this worked and I then saw the MSFS update.
…
yes, the MS Store is crap.