Hiya @SeBo1020, thank you for reaching out! I believe that I can provide some insight and I also would like to look into the crashing issue you're experiencing with Valhalla.
To answer your question, that is not currently a setting for our launcher however, closing the download pop-up window will prevent the automated launch of the game. If you don't mind, can you try that and make sure it works for you? If this does not help, we can submit a new report for that issue and get it fixed.
As for the crashing issue, I have some troubleshooting steps for us to work through and if this crash still occurs after they are completed I have a few follow-up questions. Please proceed with the following:
Unplug any unnecessary peripheral devices (Oculus, microphones, LEDs, cameras, etc)
End all non-essential background processes that are running (overlays, recording software, third-party programs, etc)
Install Valhalla and Ubisoft Connect launcher on the same drive as your OS
Verify game files
For good measure let's make sure everything in this FAQ is completed as well
After those have all been completed successfully, please launch Valhalla again and see if it crashes again. If the crash occurs again, please login to our website and create a new support case for this issue. To save time, please attach your DxDiag and MSInfo files to the case and you can also link to this discussion thread. Once received, an agent will be able to review everything and then follow up with you directly. Thank you!