Storage Report
The Storage Report shows the current count of Record and Documents per Record Type in the system. It also shows the deleted Record and Documents.

You can click the Refresh button to re-run the report. This button will not be visible until the report finishes loading.
You can click the refresh link to the right of any given Record Type name to refresh the counts for ONLY that Record Type. This link will not be visible until the report finishes loading.
If you click the Trash Can icon for any given Record Type, that will purge the deleted Records and all their Documents. If you use the CTRL key while clicking the icon, that will purge all deleted Documents from the Record Type - even from the active Records.
Records Without a Record Type
The last row, System Records/Documents, is everything left over once the Record Type rows are taken out: records that belong to no Record Type. Most of them are system records created by integrations, such as Branding images, Importer and Exporter configuration backups and AI results, and those are expected there. If the count is larger than that, some records were probably orphaned when a Record Type was deleted while it still had records in it.
Full administrators see a See which records link on that row; it opens the Records without a Record Type screen in a new tab, which lists the orphaned records, offers to restore the deleted Record Type they came from, and can move them into a Record Type or delete them.