I'm currently looking for a way to change / hide the default WordPress admin-ajax.php URL. I want to do this to remove the admin from it to prevent misunderstandings by my customers when I use the AJAX URL to read for example a file from my server. In this case, the URL has the admin prefix which is a bit confusing.
So in result the AJAX URl should looks like this: ajax.php
I've searched a bit but I can't find any helpful information. Because of this I can't show you any related code. But when I got it, I'll update my question to help other people.
Alternatively and perhaps more effectively you could leverage WP API and create a custom endpoint to process your data so that there isn't url confusion.