How to reconnect classic site to 365 group after group was deleted

Question

So I have a site collection that is in a state where it acts as though it is connected to an Office 365 group, but the group doesn't exist and the "connect to group" menu option is missing. This is causing several minor issues throughout the root site. This is what happened:

1. Connected site to Office 365 Group.
2. A week later, someone deleted the 365 group, which then deleted the connected site collection and all of our solutions therein.
3. The site collection was subsequently restored, the group was not.

So, are there PowerShell commands or site properties I can use to clear the references to the nonexistent group and either leave the site in classic or allow me to "connect to group" again? Reconnecting to a new office 365 group is my preference.

Answer 1

How did you restore the site collection? Create a new modern site collection with the same name?

For your issue, I suggest you restore the old Office 365 group.

If you've deleted an Office 365 group, by default it's retained for 30 days. This 30-day period is called "soft-delete" because you can still restore the group. After 30 days, the group and associated content is permanently deleted and cannot be restored.

To restore the Office 365 Group, you can go to Office 365 Exchange Online admin center, then select recipients, and then choose groups. You can view whether the group is Active or soft Deleted. If the group has been permanently deleted, it won't be listed at all. Select the Office 365 group you want to restore, and then choose the restore icon.

More information, you can refer to: Restore a deleted Office 365 Group