i have not use rails after 4. so a bit confuse now. this is the new way handle js, imho, looks ok until now. How this will work with images, css?
If I use a js library that also has css, how this will work, or If I use some css theme with some js library?

can I used both of them, for example
use Importmaps to load any js library, and esbuild to load css libraries?

It looks a mess for me. Everyting tangle and connected and impossible to remove.
 - importmaps => no idea of css
 - esbuild
 - webpacker
 - sprockets
 - and another library to replace sprockets in 10 years.

a mess.

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.