I can not save the game because of some artefacts in the screen save location, see the attached image

Someone playing the steam version had the same problem and finally noticed that it was caused by Bit Defender blocking the save process (probably misjudged it as malware). The solution was to create an exception for the game in Bit Defender.

So if someone has the same problem I suggest to create an exception for the game in the antivirus software you're using.