A picture is worth a 1000 words. Screenshot.
(If you can't see the picture, it shows that the transparent areas around the start menu are showing black.)
I am using:
Windows 10 Enterprise (19041.vb_release.191206-1406)
(aka Windows 10 Pro 64bit with 2004 feature update)
WindowBlinds 10.84 (059 - Windows 10 Edition) - 64 bit OS
Start10 Version 1.94
And I have 3 versions of the Atheros Pro Theme (this issue occurs on all of them.
I can temporarily correct the issue by unloading WindowBlinds and reloading.
Also I can temporarily correct the issue by switching from one Atheros version to another.
The issue returns after a reboot.
This issue appeared after I upgraded windows with the 2004 feature update.
Hopefully your developers can come up with a fix soon.
Thank you for your time.