Finaly after a week MSFS is reinstalled. The most helpfull answers in this thread where in lose order:
I could not find the failure but this is how it got fixed on my system:
1) started the installation from the xbox app. I chose the default directory on c:\ (wich by the way can be selected from the xbox app very easily). I did so from day one.
2) when the installer stopped I closed the flightsim.exe via the taskmanager. Thats because even when closed it played music and you can see that it is still running in the background.
3) most of the time it looped when installing files regarding c152 or the airport lzdr (or something like that). So I deleted those files and the folders several times in the last days.
4) after many tries it run thru. It was a crawaling race from package to package 😻
Since I did not overclocked my i9 10900k one thing I noticed. IF you have overclocked your system AND have the same problem. DADs advice is well worth a try. Reset your BIOS to default. You can oc later again. The decrypting of the files taxed my poor little 10900 in peeks more then flying in 4k on ultra/high. 😂 Which seems ridiculus to me but it is what it is. I overcklocked my cpus all the time for FSX and P3D. And if needed I will for MSFS (thats why I have the k-version). But since last week every thing whent super smoth for me and I still dont feel the urge to oc. The 10900 is a beast in stock configuration. I did oc my 3060 🤫.
Ohh and first start of the sim after install it crashed. (First time for me). Just ran the savemode, closed the sim, restarted my computer an done. Next weekend I will reinstall the PMDG DC6, Kodiak, and bijan-seasonsmod. If I feel adventures I will also reinstall the brilliant "we love VFR" mods from Puffin. And mybe some ships too.
Big shout-out to DAD, DylanM, rayharris108 and every body that did try to help. You guys rock 🤩