I just installed Qxygen quickstart according to the video you supplied for the installation. The only change I implemented was to make the site multi-language (German and English US) and I installed JCE.
I then updated Joomla to version 3.8.12, updated the recommended modules (RokSpocket -> thank you Manolis!) but could not update Unite Slider -> I will ask Ivo

Now the site is working but the Oxygen template page has no menu and content between header and footer. Not even the image placeholders -> screen shot attached
Can anyone tell me what I did wrong? I have supplied the site information.