I have a problem with the 'From the Desktop' section of 'Launching Opus' preferences. I have this set to 'Bring the last active lister to the front'. When I reboot my computer, although this setting is still checked, double clicking on the desktop does nothing. I have to check 'Disable', apply it, then recheck 'Bring the last lister ... Checking 'Open the default lister' makes no difference.
Something may be blocking dopusrt.exe from launching at startup (e.g. Windows Defender or other antivirus).
It would also happen if you ran Opus elevated via UAC as (like Explorer) Opus needs to run in the same context as the desktop. (You can use Admin Mode within Opus to perform elevated actions without elevating the entire process.)
How can I find out if anything is blocking dopusrt.exe?
Check Windows Defender first.
Also check any antivirus or security products you have which may block things. Or tools like Autoruns which can disable startup programs.
Since the blocks are implemented by individual tools, and I don't know which tools you may have on your system, I can't give exact instructions as it will vary depending on what is blocking it.
(This is assuming something is blocking it. It might not be.)
Another possible cause of the problem is that you are running Opus as administrator (i.e. elevated via UAC). You should not do that; instead, use Opus's Admin Mode. Details here.