Cannot open new project

Hi all.

My Scrivener is the latest version. I startet a project eight weeks ago und synchronised it with Aeon Timeline. Works fine.
So now I used the finished project to create a template for the next volume of the series and used it to create the new project. Which I now cannot open because it uses - so the little pop up window claims - an older format. I am asked if I want to update the format. A copy would be saved at the same place.
I click ok and I think I might do this til the end of all days because nothing happens except for a lot of copies. The project won’t open.

What is wrong and what shall I do?

Oh and if I close Scrivener (which was open with a completely different novel) it just opens the project I last worked on - not the template nor the new one.

For now I just copied the first volumen, gave it a new name und this one opens. But using my templates doesn’t work anymore.