Offline Items? How do I remove/remediate them?

In fact the 30 days window is from a "view" perspective in the desktop app.
If you look online (web browser to see the server side), you will see older deleted items remaining.
On server side, the deleted items are automatically purged after 1 year (or 365 days).
The deleted items "work" the same way as the Recycle Bin of your system (Windows typically).

However, you can permanently delete one or multiple items at once:
For that go to the Deleted Items, select one or more items, right clic and choose the option in the menu.