Nothing to do with this has changed in Opus.
When you right-click (I assume this is what you're doing, even though you don't specify) on a file, Opus consults the list of installed context menu extensions in the system in order to build and display the context menu for the file you clicked on. Most likely some program you installed or added at around the same time as you upgraded Opus has introduced this delay. Another option is that a shortcut in your Send To folder is pointing to a network location that's no longer available.
If you follow the steps in the Crash, exit or high CPU when right-clicking certain files FAQ you should be able to work out which context menu is causing the delay, and then uninstall or disable it.
Incidentally, you can use the toolbar buttons to access functions like Rename or Delete, so you don't even need to right-click the files if that's all you want to do.