Or use the Etcher AppImage to burn the .img.gz https://www.balena.io/etcher#download-etcher
Thank you very much for the hint.
Did believe that I have to return to Windows to actually burn this image.
They should officially point out on their download page, that the image could be written with every generic USB creator on LINUX.
Only a small issue, but it will prevent a lot of people to test LibreELEC from my view.