Just to advise - I have fixed it… sort of.
For reasons I can’t quite understand, Flight Simulator now only works if I ‘Run As Administrator’ (though I am sure I tried that earlier and it didn’t work!)
When running as admininstrator, a similar popup appears but (instead of the ‘Microsoft Store Package Dependency Installer’ shown in the screenshot above) I get this:
I believe the above is normal, as you often get those pop-ups when attempting to start programs as an administrator.
However, attempting to run Flight Simulator without going through ‘Run As Administrator’ still results in both of the popups in my initial post, including the ‘request is not supported’ error, and FS does not load.
I can live with it, but it would be nice to know what the cause of this is.
One thing I have reaslied is that, in order to get the add-on Self-Loading Cargo to run (as per my original post) I had to load up FSUIPC7 yesterday - FSUIPC had been installed for a while but yesterday was the first time I actully ran it (crucially, yesterday I ran it after FS had already loaded up, so today is the first time I have loaded it up since running FSUIPC for the first time).
Therefore, I’m wondering is FSUIPC has changed something which has caused the issue.
I’d welcome the thoughts of anyone with any technical know-how.