Robin, yes, as Tom again clarified, if he has an updated Windows, FS9 won't work which is exactly what I said.
The most likely and highly probable reason for his issues is not having the patch and crack installed.
I rarely bother with Windows advice because it's just too hard to get things through to people here.
FS9 also does not run perfectly under Win 11 as you suggest. As I have said in the past and been the only one to discover, Win 10/11 made FS9 unusable on likely any system running internal graphics. That's a serious issue!
Yes, you can run in a compatibility mode and as admin and it's a workaround but this is the last thing anyone should do with a program that interacts with so many other add-ons.
People absolutely will run into problems at some point.
Anyhow, I just make sure my PC is sorted. I've done this and have a perfect FS9 on Win 11 now running literally everything I have ever tried including masses of payware add-ons.
It takes a lot of work to get to this point.