BuddyPress.org

@puresaian To mention all group members simultaneously, you must implement a custom solution. This could be a special shortcode or command that automatically translates into individual mentions for all group members when used by the admin.

/**
 * Handles the custom mention "@everyone" within BuddyPress groups.
 * When @everyone is used in a group's post or comment, it replaces it with mentions of all group members.
 */
function wbcom_custom_everyone_mention_handler( $content ) {
    // Check if BuddyPress is loaded and @everyone is used in the content
    if ( function_exists( 'groups_get_current_group' ) && strpos( $content, '@everyone' ) !== false ) {
        // Get the current group details
        $group = groups_get_current_group();

        // Proceed only if we are in a group context
        if ( $group ) {
            // Fetch all members of the group
            $group_members = groups_get_group_members( array( 'group_id' => $group->id ) );
            $mentions = array();

            // Loop through each member to build the mentions array
            foreach ( $group_members['members'] as $member ) {
                $mentions[] = '@' . $member->user_nicename; // Prepares the mention syntax for each member
            }

            // Replace @everyone in the content with the individual member mentions
            $content = str_replace('@everyone', implode(' ', $mentions), $content);
        }
    }

    // Return the modified (or unmodified, if no changes were made) content
    return $content;
}

// Add filters to apply the custom mention handler in different BuddyPress content types
add_filter( 'the_content', 'wbcom_custom_everyone_mention_handler' ); // For regular WordPress content
add_filter( 'bp_activity_new_update_content', 'wbcom_custom_everyone_mention_handler' ); // For new BuddyPress activity updates
add_filter( 'bp_activity_comment_content', 'wbcom_custom_everyone_mention_handler' ); // For comments on BuddyPress activities

It’s not a tested code; it’s just giving implementation directions.