@Vanguard3000.
Okay, DiapDealer has graciously rebuilt the qt windows plugin one more time, removing the need to deal with any registry stuff.
You can grab it from here:
https://github.com/kevinhendricks/Bu...nMac/releases/
It is again called qwindows.dll.zip (I replaced the previous build).
Unzip it and use it to completely replace the previous version in the same location as before.
Then give a fresh startup of the debug Sigil a try.
This version uses exactly the same information used by Qt 5.12.X as used in Sigil-1.9.30 and appends it to the serial number to hopefully make them unique.
If Sigil 1.9.30 worked properly, this one should too.
Please let us know.
Thanks!