Admin slow on Postlist (over 30k Posts in Database)

Perhaps this filter can help you to modify the query for the specific post type and inside wp-admin

as per the documentation, this filter is called before the query is executed so you can modify/optimize the query with the help of this filter.

do_action_ref_array( 'pre_get_posts', WP_Query $query )

further reference: https://developer.wordpress.org/reference/hooks/pre_get_posts/