I'm sorry, I forgot to delete it.
I suddenly had two downloads in the Itch.io app and when I wanted to start the game, the place where I installed it opened and let me choose between the older and the new version but without a game exe or something like that.
I deleted the old version data and could play again.
However I think I have it twice in the libary. I think it was true when they said the itch.io is kinda broken.
However it feels better to download what I can this way.
Did this made it clearer?