and everything works fine, except maybe the 10m mesh
which often makes micro cuts, but the 20m is going very well.
Yes, of course the 20 m version works better, but the 10 m still works reasonably well and in fact, according to your report, it's doing only micro stutters, that's normal. That's why we have a 20 m version to choose from.
I also bought the mesh on the MSFS store and there it is the disaster
Please clarify: you bought the same scenery twice, on Simmarket AND on the MS Store ? No wonder it's a "disaster": it's possible you know have TWO mesh installed at the same time, the one from the MS Marketplace and the one from Simmarket.
The issue is, all products bought from the MS Marketplace always install in the "Official" folder, while products bought elsewhere installs in the "Community" folder so, if you bought a product twice, it's possible to get two versions installed at the same time.
If this is the case, remove the MS Marketplace version using the Content Manager, and leave only the version in the community folder, which you can choose between 20 m and 10 m.
Of course, even when using the FSDT/Simmarket installer, be sure you don't install the 10 m and the 20 m versions at the same time. If you switch from a version to another, you MUST Uninstall the one you don't use. Don't worry about activation, you can uninstall/reinstall an unlimited number of times on the same system, the only time you need to reactivate, if if you change major hardware components or reinstall Windows.