Select Members of Selected Groups

This is a command that is found in the gear menu of the Groups inspector. Select one or more goops in the list of groups. Using the ‘Select Members of Selected Groups’ command will select all the channels that are contained in the group(s).

Overview of groups in Logic Pro — Apple Support

Prior to mixing, you may find it useful to define some logical channel strip groups. You could, for example, group all drum channel strips under one drum group. This would allow you to control the group meters (volume, pan, mute, solo, sends, and so on) using a single control, while still maintaining the relative parameter values of each channel strip.