Win 11 Pro
Opus has added its icon to 'Open' in the Windows context menu for folders, while that option specifically does not open in Opus (with all replacements in place):
I suppose that icon is supposed to be next to 'Open in Directory Opus' instead, if anything.
It's a File Explorer bug, not an Opus one.
Good luck getting Microsoft to fix it though. 
Oof, interesting. How do they obtain the icon if it's not provided by Opus in some way? 
Unless the MS bug is that it gets misplaced, in which case it's probably better to not have any icon there to prevent the confusion. 
When they choose which icon to show next to the menu item, the shell isn't paying attention to its own flags for saying a filetype action doesn't apply within Explorer windows.
They're only doing that when choosing which action to run after you click it.
It's funny to see that even Microsoft can't remember all the complexity they've layered into the filetypes and context menu systems over the years.