Yet no matter what I try, when I go to delete what’s causing them, the delete button is greyed-out!
Can anyone help? Is there a way to force delete it? Possibly a way to delete the package that had the files that caused the errors?
Usually packages are moved to UPM for clean version management, so it’s likely the UPM version is what you want. Use your OS’s file browser to delete (or recycle if you want to be able to recover the files) the Assets/Oculus folder, which seems to store non-UPM versions of what is now stored in UPM packages.
Alternatively, if you go to the Project view in the editor, there should be an entry at the top named Assets. You can right-click that and show it in your file browser that way.
The Oculus folder should be inside the Assets folder.