A “soft delete” of a user account in Microsoft Office 365 means that the user account has been deleted in the usual way and so Microsoft keeps it around in the office 365 recycle bin for 30 days. You can manually flush the recycle bin to get rid of it if you really need to, but it costs you nothing and it gives you the ability to restore that account including the mailbox in the next 30 days.
If you delete a user account using the Microsoft 365 Portal, or you use the PowerShell command:
Remove-AzureADUser -ObjectID [name]
ie. Remove-AzureADUser -ObjectID johnnydel
That account and the data associated with it in a mailbox or in OneDrive or in SharePoint is not actually deleted it simply flagged for deletion and moved into a virtual recycle bin.
How To Restore A Deleted Microsoft Office 365 Account
You can also restore deleted Microsoft 365 user accounts via PowerShell without too much difficulty. Click HERE for those details.
As shown in the above screen shot you don’t see the users that you have deleted recently that probably means you remove their license and that means they don’t show up and deleted users. Microsoft calls this a heart delete even though they’re still there for 30 days.
Currently, removing the license leaves the mailbox in a hard-deleted state. Therefore, the mailbox is not displayed as either Soft Deleted or Inactive.https://learn.microsoft.com/en-us/exchange/troubleshoot/user-and-shared-mailboxes/no-soft-deleted-mailbox-after-license-removal
If you want to restore a user that’s been hard deleted within 30 days it’s pretty easy to do. Most notably you need to assign them a license and then you can restore them.
Easy instructions on how to restore a hard deleted user and mail box are available directly from Microsoft HERE.