If you type /dopusdata/ConfigFiles into the Opus path field, then open prefs.oxc and search for </fonts>, just above it there should be a line line the one highlighted here:
If the opening tag on that line is <code,> instead of <code> then the config file must not have been re-saved since 12.9.3 was installed. (See my previous reply for what to do in that case.)
If it has <code> then whatever is happening is a separate issue:
What are you settings under Preferences / Launching Opus / Explorer Replacement?
Do the main Opus window titlebars say "ADMINISTRATOR"? If so, the whole dopus.exe process is running elevated, and UAC will block Explorer Replacement from functioning.
Does the problem affect all folders, or just ones on the desktop?
For the explorer replacement preference, I have the 2nd option selected (replace Explorer for all file system folders.
I don't have DOPUS running as administrator/elevated.
This happens from the desktop when I double-click on a folder. If I find a folder through the start menu, such as My Documents, and open it normally it also opens in Explorer and not DOPUS.
You're not using a portable install or anything like that?
It sounds like either the Opus DLLs involved in the context menu and explorer replacement are not installed or something on your system has disabled or blocked them.
Could you show us a screenshot of these two Preferences pages?