I solved the problem.
On installation windows asks if roon should be allowed for public or private network.
The default is public and on first installation I changed it to private.
This was the mistake and I was not able to enable the chromecast devices (I have only those).
Uninstallation and a new installation was not succesful because Windows remembered this adjustment to private network.
So I changed the settings in the “windows defender firewall” menu concerning apps from privat to public and now everything works.
Also, I was not succesful to connect the android app to the windows roon core before this adjustment. Now this is also working.
So at the moment everything is working fine.
