Hello Marcin!
Thanks a lot for taking the time! @MarcinBajor
I just tryed it on another 3B+ with Raspbian allready installed and running for a few months (with unchanged swap-file size), and it did crash trying to install (saying one of the packages could not be installed).
I will try with another clean install on another card later (first with the regular swap file, if needed with a manually maxed out swap file).
Thanks again and all the best,
Alex