I’m not sure if this is a bug or a feature, but when you’re an admin, even with highest permissions, you cannot delete a folder if someone else created it. Even lower permission users.
The best an admin can do is rename the folder with something like “Delete Me”. Since it’s not a board, it does not contain a log of who the creator was, which means finding them to request deletion can be difficult.
I’m unsure if this is a bug or a feature, but the ability to delete/alter pretty much any thing is essential for those with admin/owner rights so they can moderate the system appropriately.