After installing Onyx I received the following error:
Running an insider preview build might be the problem here but should not be one. Maybe Onyx demands this specific version of .net, ignoring any newer versions.
Cheers,
VJS
Update to the newest insider build. This was a bug from Microsoft and got corrected
Thanks for your effort to get onto this topic that fast.
Much appreciated 
Please share if that fixes it.
I had a lot of problems with the insider preview and rolled back. Not with Onyx but with the file explorer.
Updating to a newer preview build did indeed fix the problem.
I did not have problems with the file explorer, maybe because I am using the slow channel of the Insider preview.
Cheers