There's a big red circle around the folder that was highlighted that DO wouldn't delete in case you didn't see it. It's not relevent what folder, just a folder in the folder tree won't delete using the delete button. I have to delete using the context menu. I don't recall this being an issue in any other DO version.
@enableif:=true
@if:!Set FOCUS=LeftTree
Set FOCUS=Left
@if:common
Delete
If the left tree has focus, it will delete from that. Otherwise, it will delete from the left file display.
Note that if you're renaming something in the tree and click the button, it'll act on the file display and not the tree (since the tree doesn't technically have focus at that time, and it's what the command tests).
The @enableif line at the top is so the button is always enabled. Otherwise, the Delete command would disable the button if the active file display doesn't have anything selected.
It has worked this way for as long as I can remember, and isn't a bug. Your command was explicitly setting focus on the left file display before running the delete command. Opus was doing exactly as it was told.
What I'm trying to accomplish with the Focus is to prevent accidental deletes on the right side or vice-versa but I want to be able to delete in the folder tree or the file list.