I did play the full game and it did work expectedly well (the game has quite a few known minor glitches, nothing actually game breaking). Only then at the very end the actual ending video sequence did play, but after that there should play a let's call it epilogue video sequence followed by the credits which instead did just show a black screen that could only be closed with Alt+F4. Reloading the save game, just ended in the same issue again.