I think this is a male lace weaver spider in the genus Amaurobius
Thanks a lot for the clue! I reckon it’s an Amaurobius fenestralis – https://wiki.arages.de/index.php?title=Amaurobius_fenestralis / / https://www.natur-in-nrw.de/HTML/Tiere/Spinnen/TSP-34.html – as the pattern on the ophistosoma fits.
Have a look at A. similis also. They are very alike.