Zombie files/folders from non-existent Federated sharing

Files have been shared using Federated Share protocol with me by another server. That server has since been removed (from the internet). Shared files and folders are still visible in my NC instance but they are ‘zombies’. I cannot download, rename, delete or move them.
How do I clean these files from my system?

Note: At the time of sharing, both servers were NC11. I have since upgraded to NC 12.

I was testing federating sharing in our test environment, I shared to an external source, my own Nextcloud server. It worked, but now the test server is deleted. I stumbled upon the same issue as conspacer. I have a zombie Nextcloud.mp4 (this is the file I used for testing) in my root Nextcloud folder. I’m unable to remove the shared file, Nextcloud gives an error:
“Error deleting file: Nextcloud.mp4”
But what’s really annoying, I got a new laptop, tried to configure the Nextcloud client, but the client kept on trying to sync Nextcloud.mp4. Because this file is in the root, it cannot be deselected in the sync client.

Is there any way to manually remove the federated shared file? I do think that a force delete option if the other side isn’t available anymore is really needed it this case.
seeing that this behavior will get ugly in bigger hosting environments.

An option to disable or enable loose files in the root Nextcloud folder would also be nice.
Anyway, since this was only a single Nextcloud.mp4, file, my workaround by adding this file to the ignore list works, but I really want to remove the shared file.