By default, we do not have this option. You can use the following function code. Please see the steps below:

Note: Make sure to have a complete site backup before proceeding

    1. Go to Appearance - Theme File Editor.

    2. Under Select theme to edit, choose (BuddyBoss Child/whatever theme is active), then click Select.

    3. Below Theme Files, select Theme Functions (functions.php).

    4. Append the code just before the closing PHP tag “?>”:

function bbg_set_group_default_extension( $ext ) {
    return 'messages'; // Set the default extension to 'messages'
}
add_filter( 'bp_groups_default_extension', 'bbg_set_group_default_extension' );

    5. Click Update File to save the changes.

Note: Any modifications are considered as custom work already. Know more about our Support Policy here: https://www.buddyboss.com/support-policy/

Screenshots

Without Code (when opening the group, the default tab is Members):

With Code: