Option to only allow existing guest accounts to be added
In SharePoint, sites can have the following setting:
"This site can only be shared with existing external users who sign in"
Unfortunately, this setting has no effect on the Team above this site - you can still add new users.
Especially when you're using a controlled invitation/approval process (via the Azure B2B) you don't want your end users to be able to add new guest users via the "Add member" button.