Microsoft 365 backup:
If content configured for backup - such as Planner plans - is shared within a Microsoft 365 group, it will be backed up through the Planner backup process.
If the group is connected to Microsoft Teams, then Teams conversations and files shared within the Group are also backed up and visible under the respective Team, provided the relevant services have been enabled for backup.
Entra ID backup:
Microsoft 365 groups - including all their attributes, members, memberships, and role assignments - are fully backed up as part of the Group backup process in Entra ID backup.