This section is available in the Adguard window (see the Settings - Browsers section) only if the extended interface is enabled.
This section allows you to select the browsers where all traffic will be filtered or, rather, intercepted using a special traffic interception module. More information about the traffic interception module is available in the Network settings section.
If the browser you use is not on the list, ou can add it manually. To do that, click the Add browser... button and find the executable (*.exe) file of the necessary browser in the dialog window.