Shows how to add a custom order value to a connection to order by a custom field.

order-by-acf-like-count.php

add_filter( 'graphql_PostObjectsConnectionOrderbyEnum_values', function( $values ) {

	$values['LIKE_COUNT'] = [
		'value' => 'like_count',
		'description' => __( 'The number of likes on the post', 'wp-graphql' ),
	];

	return $values;

} );

add_filter( 'graphql_post_object_connection_query_args', function( $query_args, $source, $input ) {

	if ( isset( $input['where']['orderby'] ) && is_array( $input['where']['orderby'] ) ) {

		foreach( $input['where']['orderby'] as $orderby ) {

			if ( ! isset( $orderby['field'] ) || 'like_count' !== $orderby['field'] ) {
				continue;
			}

			$query_args['meta_type'] = 'NUMERIC';
			$query_args['meta_key'] = 'like_count';
			$query_args['orderby']['meta_value_num'] = $orderby['order'];

		}

	}

	return $query_args;

}, 10, 3);

@mickras I never ended up finding a solution, so I had moved back to the Wordpress REST API and created my own search filters