I do have a question regarding retention policies on o365 groups and what happens to it after deletion. As I was testing my group, I deleted it, I was able to see it as softdeleted via get-unifiedgroup but I couldn’t see it as inactive mailbox anywhere, couldn’t pull mailbox statistics as well. I wasn’t able to do content search as it couldn’t find it. Am I missing something here? I thought mailbox would be preserved after deletion - like shared or user mailbox.
You won't "see" it, as it's not a "regular" mailbox, so it's not returned in the output of Get-Mailbox -InactiveMailboxOnly. It will however be preserved for the duration of the retention policy and can be searched via eDiscovery. Prefix the entry with . when performing an eDiscovery/Content search or just do a blank "include all" one.