bp_activity_format_activity_action_activity_update( string $action, object $activity )

function bp_activity_format_activity_action_activity_update( $action, $activity ) {
	if ( bp_activity_do_mentions() && $usernames = bp_activity_find_mentions( $activity->content ) ) {
		$mentioned_users = array_filter( array_map( 'bp_get_user_by_nickname', $usernames ) );

		$mentioned_users_link = array_map( function($mentioned_user) {
			return bp_core_get_userlink( $mentioned_user->ID );
		}, $mentioned_users);

		$last_user_link = array_pop($mentioned_users_link);

		$action = sprintf(
			__( '%s <span class="activity-to">to</span> %s%s%s', 'buddyboss'),
			bp_core_get_userlink( $activity->user_id ),
			$mentioned_users_link? implode(', ', $mentioned_users_link) : '',
			$mentioned_users_link? __(' and ', 'buddyboss') : '',
			$last_user_link
		);
	} else {
		$action = sprintf( __( '%s posted an update', 'buddyboss' ), bp_core_get_userlink( $activity->user_id ) );
	}

	/**
	 * Filters the formatted activity action update string.
	 *
	 * @since BuddyPress 1.2.0
	 *
	 * @param string               $action   Activity action string value.
	 * @param BP_Activity_Activity $activity Activity item object.
	 */
	return apply_filters( 'bp_activity_new_update_action', $action, $activity );
}