If you have problem with:
POST wp-admin/admin-ajax.php 500 in WP
define( 'WP_MAX_MEMORY_LIMIT', '512M' ); in wp-config.php
max_input_vars = 6000 ; in php.ini
and deactivate all plugins and active one by one until you see which plugin is causing problem.
(Ps. have the great chance to be the Yoast SEO plugin the problem)