Short version:
Microsoft are introducing a change in access behaviour for public groups in Microsoft Forms. Currently all users can edit a public Group form and view response data without joining the public group 😱  This change means they would need to join the Group to do this. Due mid- to late March 2021.
Details:
Microsoft are introducing a change in public groups that affects Microsoft Forms users. Currently, all users in an organisation can access a shared form in a public group (Microsoft Office 365 Group marked as public). All users can edit the form and view response data without first joining the public group.
After this change, users will need to join and become a member of a public group in order to access shared forms within the group.
Availability:
This feature rollout will begin mid-March and should be complete by late March 2021.
Links:
Related blog: Share a Form.
