This is a must for me, and it's not obvious to me how to do this operation.
Preferences > Launching Opus > Explorer Replacement
Where does it say, "Launching Opus" in Preferences? I don't see it?
Ok, great! Thank you. So, I've done this, but DO still is not coming up as my default "File Explorer" replacing Windows File Explorer. What am I missing?
In what context is Opus not coming up where you expect it to?
Facebook and Ourskylight.com.
If you mean File Open dialogs, see here at the top right of the page: