Perhaps I'm mis-understanding but it looks like Directory Opus and Windows 11 thumbnail caches are always being created together.
Even if I only use Directory Opus, and having cleared the Windows cache, I can still see files being created / updated in:
C:\Users...\AppData\Local\GPSoftware\Directory Opus\Thumbnail Cache
as well as
C:\Users...\AppData\Local\Microsoft\Windows\Explorer
I've tried turning off Folder Thumbnails via the Shell to see if this will stop this double creation but I don't think that is the right option / or even possible?
If Windows generates the thumbnail for Opus, it might be stored in the Windows cache.
If Opus generates the thumbnail, it might be stored in the Opus cache.
The same thumbnail will only be in one cache or the other (if it is cached at all).
If you generate thumbnails for a folder containing various types, some may end up in the Windows cache and some in the Opus cache, which is completely normal.
Because Windows, or shell extensions, generate the thumbnails for some file types.
PDFs are one example. Opus doesn't generate PDF thumbnails itself; it leaves it to the installed PDF software to do so, via the standard Windows mechanism.