There is a syntax bug in the installation script. I solved it, but only locally and not in the repository (silly me 👎). The Github user prbt2016 provided a pull request and I will release a new version later today. If one wants to upgrade the own forum before the new release, one has to add a single bracket in
install/index.php, line #45 as seen in the code on Github.
Pay attention to the section between
die('Error in line.
I'm sorry for the inconvinience.
Trenne niemals Müll, denn er hat nur eine Silbe!