how rewrite pagination URL views for SEO?
In Drupal 7 you can use Query Parameters To URL but the D8 port needs more work. Maybe you can help with that in the course of the work for your current project? 

It's similar with Clean Pagination that cleans up the pagination specifically, D8 needs more work. 

In the meantime maybe you can replace some of the exposed Views filters with contextual ones, they take arguments separated with /. 

With a Contextual filter you can display a Summary of taxonomy term names at the top of your views (or any region for that matter) instead of an exposed filter with the term names. That way you would see a list of terms as links at the top of your Views, and the links paths would look like mypath/cat. 

Pagination would still add ?page=1 so you'd have mypath/cat?page=1 unless you get the Clean Pagination running.