This is great low-level howto, thanks for it!

Avada developers however anticipated that not everyone would need those two post types and provide a way to remove them. It's kinda convoluted but it's probably better to follow the way supported by the developers if you intend to build your site on Avada.

See here for steps: https://theme-fusion.com/forums/topic/remove-disable-hide-faq-portfolio-comments-in-backend/

In a nutshell, they provide a "Avada Custom Branding" plugin which has (among other things) a checkbox for removing the custom types registered by Avada.