I have already upgraded to Rails 8 and am currently writing a guide on how to use Propshaft (because I was unable to find important infos). It‘s far from ready, but I plan to include a wizard that allows you to select your needs and it spits out the combination of jsbuild/cssbuild/importmaps/dartsass that you need.
In short: if your application only needs distribution-ready JS and CSS (from libraries like Bootstrap, Splide or Lightbox2) you only need importmaps-rails.
If you use SASS, you need dartsass-rails. And if you need to compile TS (with esbuild or webpack) you need jsbundling-rails.
Especially the first case got a lot easier with Propshaft.
In short: if your application only needs distribution-ready JS and CSS (from libraries like Bootstrap, Splide or Lightbox2) you only need importmaps-rails. If you use SASS, you need dartsass-rails. And if you need to compile TS (with esbuild or webpack) you need jsbundling-rails.
Especially the first case got a lot easier with Propshaft.