Testing the most recent spacedesk Driver on Windows 11 worked so far on our side.
Both screen mirroring and extension should work.
Since Windows 11 is not yet officially released, I assume your Windows 11 is still an Insider Preview version.
And maybe it’s possible that it’s a Windows 11 bug.
We will keep an eye on this issue and check if we can reproduce it on our side.
By the way, did you already tried our most recent spacedesk Driver v1.0.15 on the web https://spacedesk.net?
For further analysis, could you please run dxdiag.exe on your primary machine, click “Save All Information”, then attach the output file (dxdiag.txt) on your next reply.