use-acfs-load-field-filter-with-advanced-forms.php

<?php

add_filter( 'acf/load_field/key=TARGET_FIELD_KEY_HERE', 'afp_test_acf_load_field_filter' );
function afp_test_acf_load_field_filter( $field ) {

	$field['choices'] = [];

	// Using get_posts() instead of WP_Query prevents query loop issues and global var overrides that break
	// functionality on the advanced forms edit screen and potentially other contexts.
	$posts = get_posts( [
		'post_type' => 'post',
		'posts_per_page' => - 1,
		'orderby' => 'title',
		'order' => 'ASC',
	] );

	foreach ( $posts as $post ) {
		$field['choices'][ $post->ID ] = get_the_title( $post );
	}

	return $field;
}