@etorreborre I think I found the cause of this when I was working on the other direnv response for you.
It looks like flox isn’t detecting non-interactive shells, so if you have multiple envs in a project ( the default + any package ) it will try to prompt you to select. You won’t see the prompt because it’s not an interactive shell, and it’ll just hang.
If you instead explicitly use . <( flox activate -e '.#default'; ); it shouldn’t hang.
I’ve filed a bug fix ticket for this so hopefully we can get it resolved soon.