Is there a way to add all users to a new team at once.
I figured out a way to do it. You have to be account admin for this method.
Go to Organization Settings → Members and in the lower right corner click “Export membership data”
This will email you a file with all members and their emails. Copy the email address column and paste it into the invite box for the new team.
I got something a little bit easier I believe → Asana Everyone, add every members on a task, project or team
It will add all members, not guests.