Image Search not working with custom query

What is it that you are trying to achieve with this code? Are you trying to exclude pages from website search results?

If so, you should use something like this:

add_filter(
	'register_post_type_args',
	static function ( $args, $name ) {
		if ( 'page' === $name ) {
			$args['exclude_from_search'] = true;
		}

		return $args;
	},
	10,
	2
);

I only want posts to show in my frontend site search, not pages or custom post types.

Unfortunately the ‘exclude_from_search’ attribute causes issues with the custom post type taxonomy archive pages, which is why I prefer to use the custom query instead.

I see. Well, in that case if you wanna keep your existing snippet I recommend simply not altering any REST API requests by checking for the REST_REQUEST constant.

For example like this:

function purrdesign_excludePostType( $query ) {
	if (
		! $query->is_admin &&
		$query->is_search &&
		( ! defined( 'REST_REQUEST' ) || ! REST_REQUEST )
	) {
		$query->set( 'post_type', 'post' );
	}

	return $query;
}

add_filter( 'pre_get_posts', 'purrdesign_excludePostType' );

Yes, that worked perfectly! Exactly what I was hoping for. Thanks so much for the quick response!