Okay, it was premature of me to add "perfectly" to the end there...
Now I the editor works, if I run it as an admin, but there's one issue. I don't know whether this is a common problem, or if there's a well known solution to it, but for me the editor alway worked as follows:
When I create a scenario with the editor, instead of copying an already existing one like a map that I want to base my scenario on, the BIQ file is not there in the conquest folder. The editor and the game both see it, meaning it's not a huge problem, and seems to be intended behaviour, so I was never too hung up about it. I tried to look for the their location both on my computer and online, but not having found anything, I just figured everyone just accepeted the reality of the situation. Which I still, think is the case, but I'm explaining this to make it easy to state my problem, and for us to be on the same page.
The editor now doesn't seem to see the scenarios that are not visible from the file explorer. They are still *somewhere*, since I checked and the gam sees them just fine, so the editor should be able to find them wherever it found them before.
Also just to report back, I checked some other launch option, and the compatibility mode seems to have no positive effect. If I launch it as admin, the editor works with that setting, even with it, the elusive files do not appear.
Thanks for all the help, mpeti