So I believe the correct answer is that Microsoft broke the transparency effect of drag and drop during the development of Windows 11. So seeing an opaque white square is technically "normal" behavior (at least in Windows 11). The most likely reason as to why they haven't fixed it is because they've already created a new drag and drop icon system to replace the old one as shown in Edwin's attached picture in
post #16. Unfortunately since we all know how slow Microsoft is with UI consistency, they'll probably fix this in 2326.
I believe if you look in the Windows 11
Accent Colorizor Github page, they have a fix for this in the parent page for that Github project (or whatever it’s called).