Why can't a user select a custom group as the team access control for a Supplier Profile Questionnaire (SPQ) question?

The custom group is unavailable for selection because the Team Access Controls for the SPQ are restricted to five options: Classified, Finance Information, Legal Information, Owner/Administrator Only, and Private to Team Members.

In order to restrict visibility while allowing the custom group to view the question, the custom group can be made a child group of one of the previously listed groups. Then, the parent group can be set in the Team Access Control field.

Please see the managing the Supplier Profile Questionnaire document for more information.

Supplier Lifecycle & Performance > Modular Questionnaire