http://valinet6l6tq6d5yohaa6gdsf2ho4qcqcxyj2nahp5kd4z7nsa6ycdqd.onion/2022/01/21/Disable-the-rounded-corners-in-Windows-11.html
Personally I like them, but a lot of people do not, and for good reason: it would have been logical for Microsoft to offer at least a hidden option to enable the legacy behavior from Windows 10, where the corners are sharp, 90-degree angle. Unfortunately, they did not, so we are once again left to scramble through their executables and see what we can find.