>>17947601
>>17947738
Found this but it was written during Weimar times. The author Hans Dominik was a famous german sci fi author who died in December 1945. He still wrote a few sci fi novels and short stories during the time of the Third Reich but none of them seem to mention aliens but I haven't researched him enough. Apparently that guy wasn't allowed to sell a novel in 1941, he published it in 1934 because it depicted a conflict between Japan and the US and americans seem to have been the main protagonists there but he was allowed to sell it again in 1943.
There was a short film called Weltraumschiff 1 startet ("Spaceship I launches") from 1940 but it didn't depict any aliens it seems. Two other films were planned. One called Weltraumschiff 18 ("Spaceship 18") which also doesn't seem to have planned no aliens and Zwischenfall im Weltraum ("Incident in space"). For both the production stopped due to WWII. I couldn't any information about Zwischenfall im Weltraum.