I created a new rails application with

rails new testapp --javascript esbuild --css bootstrap

Then ran 

rails action_text:install

I created a resource and attached an attribute with the has_rich_text and it seems to be working properly. Make sure that you have yarn installed on your system. In my case, it imported the actiontext.css in the application.bootstrap.scss

@import 'actiontext.css';

And it rendered properly.