how this will work with slim-select for example
I try to add in application.sass.scss 

@use 'slim-select/dist/slimselect.css';
@import also
I try to also add it inside of the js
neither work.

any tips here?

@use 'slim-select/dist/slimselect.css';
@use 'bootstrap/scss/bootstrap';

using this will load all of them

my issue with this is that I have no clear scenarios, or best practice, or when to use frame vs stream etc.

I think is also important that you need to have docker on the machine, and start it :)

Sorry, what I mean, when you run kamal setup from terminal(example: mac) you need to have docker up and running on your mac. AFAIK