Sorry, after rebooting my laptop everything is working fine. As you were guessing probably there was a second instance still running after the upgrade. Thank you for the help.
Do you usually change the title to something like "Solved" here?
When I try to setup the sync through google drive (which was working fine on version 5) I get the step of authorizing your app. Then the xdg-open opens enpass but a new window and the first window stay always in the state of waiting for authorization process to be complete. I attach a gif to better explain the issue