• What is the "Use Keychain" button for ?
    When enabling or disabling a resolution, SwitchResX requires you to enter your administrator password, because the settings it modifies require rights to be saved. You can use the standard dialog to authenticate, as Apple requires (they claim that new authentication means, such as biometrics, may become available in future macOS versions).
    But this dialog requires you to authenticate each time you make a modification. For this, you can also authenticate only once, and save the entered information in the Keychain, so that you'll never asked to enter the password again (but you'll loose the advantages of the biometrics if they become available).