Is it still the case that a new user to an app can only be added using glide builder? (other than sign up)
can they be added from the builder using a form? or must it be only via the data editor?
if you give an admin a dashboard to handle his app, how do you usually handle adding private users to the app? (no sign up)
Yes, users can be added via a form to the User Profiles table in the same way that you would add rows to any other table. The only complication is if you are using Roles. If the Admin user needs to assign a role to a new user other than their own (which is usually the case), then the role either needs to be set manually via the Data Editor, or via the API.