http://valinet6l6tq6d5yohaa6gdsf2ho4qcqcxyj2nahp5kd4z7nsa6ycdqd.onion/2022/01/21/Disable-the-rounded-corners-in-Windows-11.html
Anyway, by experimenting, I saw that a 0x0 there is essentially CTopLevelWindow::GetEffectiveCornerStyle returning 1 , while if we set to 0x1 … boom, we get the nice 90-degree corners from Windows 10, complete with the context menu working. Okay, so it seems the way to go is to make the radius as small as to be basically square nut not mathematically square, so dwm.exe would still think it works with rounded corners.