Sometimes when trying to delete a site and then while restoring it, it fails. You keep getting the error: "No content databases are available for this operation". You will discover that the site is not really deleted.

To check if the site was deleted use this command:

To remove the site, use this command:
Remove-SPDeletedSite -Identity xxx

The safest process to delete a site is:

Remove-SPSite –Identity
Get-SPDeletedSite (to get the deleted site identity)
Remove-SPDeletedSite -Identity xxx (to force deletion)

It should be highlighted that this is the resolution for a deletion operation that happened from the SharePoint admin console. It stayed in the deleted sites queue without being deleted. It is worth mentioning that we can start deleting the site using Remove-SPSite and if the site still pending deletion, then we can apply the rest of the commands as stated.