Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Dear Mohammad AL Khalil,
Good day! Thank you for posting your query in our community.
Per the description shared, I understand your concerna and I would like to know whether you have deleted the Microsoft 365 group that is associated with the Plan created in the Micrsoft Planner?
If yes, then I would like to suggest you restore the delete group from the Deleted Groups section of Office 365 admin center. If you haven't deleted the group, then please access the Microsoft Planner and go to All Plans to see whether the problematic Plan is present.
Thank you for your patience and understanding!!
Sincerely
Mia | Microsoft Moderator