The most useful GNOME extension on the planet. Rounded corners offer innovative advantages like less screen real estate. Saves energy on OLED screens since less pixels are lit.
Sorry, I'm currently not really willing to put too much time into that feature as that would imply making a proper configuration menu, but feel free to make a pull request.
Do not round corners between 2 displays and/or add setting to choose what corners should be rounded for each monitor.