http://valinet6l6tq6d5yohaa6gdsf2ho4qcqcxyj2nahp5kd4z7nsa6ycdqd.onion/2022/01/21/Disable-the-rounded-corners-in-Windows-11.html
I am a bit familiar with it from my work on WinCenterTitle , a program which let you center the text displayed in the non-client title bar of windows, as in Windows 8 and 8.1. Take notice, I said non-client: the compositor is only responsible for drawing the title bar of windows that do not elect to do it themselves (and inform it so).