How to get square-cornered windows back?

I resorted to using Windhawk. This tool works by injecting a small piece of code into the Desktop Window Manager to override the default corner radius without modifying your system files permanently. Once you install the application, you can search for and enable the mod titled Disable rounded corners in Windows 11. You can revert the changes instantly by simply toggling the mod off or uninstalling the app.

If you are looking for a way to force square corners without installing background utilities, you can try a high contrast theme through the accessibility settings. You can do this by pressing Left Alt plus Left Shift plus Print Screen on your keyboard. This should remove rounded borders and makes the edges of windows easier to define, but it also changes the colors and transparency effects of your entire desktop, which may not be ideal for daily use.

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hth

Marcin