See https://buddypress.org/support/topic/buddypress-7-0-0-filippi/ for context..

bp-custom.php

<?php

// Needs https://fr.wordpress.org/plugins/bp-create-group-type/ to be active.
function alersn_set_group_type_tabs( $tabs = array() ) {
	$group_types = bp_groups_get_group_types( array( 'has_directory' => true ), 'objects' );
	$terms_count = get_terms(
		array(
			'taxonomy'   => bp_get_group_type_tax_name(),
			'include'    => wp_list_pluck( $group_types, 'db_id' ),
			'hide_empty' => false,
			'count'      => true,
		)
	);

	$group_types_count = wp_list_pluck( $terms_count, 'count', 'term_id' );

	foreach ( $group_types as $type_id => $type ) {
		$count = 0;
		if ( isset( $group_types_count[ $type->db_id ] ) ) {
			$count = $group_types_count[ $type->db_id ];
		}

		$tabs[ $type_id ] = array(
			'component' => 'groups',
			'slug'      => esc_attr( $type->directory_slug ),
			'li_class'  => array( 'bpgt-type-tab' ),
			'link'      => bp_get_groups_directory_permalink(),
			'text'      => esc_attr( $type->name ),
			'count'     => bp_core_number_format( $count ),
		);
	}

	return $tabs;
}
add_action( 'bp_nouveau_get_groups_directory_nav_items', 'alersn_set_group_type_tabs' );