BuddyPress.org

I think you’ll want something like this:

add_action( 'bp_actions', 'remove_members_activity_tab', 5 );
function remove_members_activity_tab() {
	global $bp;
	bp_core_remove_nav_item( 'activity' );
}

which should remove the tab, but it’ll also remove the whole navigation if Activity is set as the default. To make sure that doesn’t happen, add this:

add_action( 'bp_setup_nav', 'change_settings_subnav', 5 );
function change_settings_subnav() {
	$args = array(
		'parent_slug' => 'settings',
		'screen_function' => 'bp_core_screen_notification_settings',
		'subnav_slug' => 'notifications'
	);

	bp_core_new_nav_default( $args );
}

This worked for me, thanks