Thanks to mads great support, I was able to finally port my website from GetSimpleCMS to Automad.
It actually became more compact and lightweight in the process and doesn't need any plugins (which was the main problem with GS, since I needed to move to PHP 7+ and the plugins I used were no longer maintained).
Here's the URL: https://www.screendream.de/
It's not responsive yet and mainly made for (fullscreen - F11) desktop use.
Maybe one day I'll get around to finally grok mobile design - I don't use any mobile devices for surfing myself... ;-)
There are still some things to optimise, especially the menu is a bit weird and needs some more thinking. But at least it works for now :-)
Thanks again for all the help!!! :-)