I used the code from demo and the scopes and form work by themselves. When I added Materialize forms, I noticed that the form and filtering doesn't anymore.
Apparently filterrific doesn't load its javascript library (I loaded Jquery for materialize, which works fine).
From my understanding
//= require filterrific/filterrific-jquery
in assets/javascript/application.js won't work (also tried).
I also get an asset error
Asset `filterrific/filterrific-spinner.gif` was not declared to be precompiled in production.
Declare links to your assets in `app/assets/config/manifest.js`.
The gem seems Rails 6 ready (says the table on github), but there is no documentation on how to make it work with Rails 6 and WebPacker.
Add the following line to app/assets/config/manifest.js
//= link filterrific/filterrific-spinner.gif