I found out, that the only font that can handle this row with two ö is times with font weight normal. If I set font weight to bold, it's not working either.
Using my search engine I found that many had good results using freesans but that doesn't work for me. I checked also my versions and settings: PHP 7.4.16, default_charset UTF-8 / mysql Ver 15.1 Distrib 10.2.37-MariaDB, for Linux (x86_64) using readline 5.1, Encoding UTF-8 Unicode, Collation utf8_general_ci.
Because that solved problems before, I increased the memory_limit in php settings to 1GB, but that didn't make a difference. Attached is a file with the error messages.
Nubuilder is an excellent tool and I would really like to generate my reports with umlauts. If somebody maybe has another hint, I would love to try it. Otherwise I'm stuck with the font "times" or without umlauts

Cheers Mike