Description of Problem: As a site admin, I would expect that custom dropdown profile fields would behave the same on the edit user profile page as the initial user creation (sign up) page. However, the behavior differs. On the sign up page, the dropdown defaults to the top option in the dropdown list resulting in false positives for the top option if users are not being careful. However, when a user edits their profile, the same dropdown has "Choose" and doesn't allow the user to move on without choosing an option and engaging carefully with the dropdown.

Impact: Automations as a result of dropdowns are common, and if users are able to default to the top option of the dropdown even when no default value has been set, this can result in the automations firing inaccurately. For Moodle Workplace specifically, this type of workflow to sort users into Tenants can be very important.

Replication Steps:

1. Create a required user profile custom field and do not assign a default value. (Image 1)
2. Note how an existing account has to update the field and "Choose..." is present. (Image 2)
3. Turn on settings to allow users to create their own accounts through email based self registration.
4. Begin the user account creation process.
5. Note that "Choose..." is not an option in the dropdown and the field defaults to the top option in the dropdown. (Image 3)

Note that this behavior is the same on all versions tested from 4.x and likely is a longstanding UX inconsistency between editing profiles and creating new email-based self registration accounts.