Upgrading Ruby - asset pipeline misconfigured

Question

I'm in the process of upgrading Ruby versions for my company, going from 2.7.6 to 3.2.2. Our app uses Rails 6.1.3 and webpacker 6.0.0. I know the webpacker gem is deprecated and we're supposed to use importmaps/jsbundling-rails but I'm saving that work for when I upgrade Rails. I'm sure something is misconfigured somewhere but I'm not quite sure what that is.

Here's the contents of my app/assets/config/manifest.js file:

//= link_tree ../images
//= link_directory ../javascripts .js
//= link_directory ../stylesheets .css
//= link_tree ../builds

Here's the output when I try to run specs:

     Failure/Error: <%= stylesheet_pack_tag 'application', media: 'all', 'data-turbo-track': 'reload' %>

     ActionView::Template::Error:
       Webpacker can't find application.css in /Users/.../public/packs-test/manifest.json. Possible causes:
       1. You want to set webpacker.yml value of compile to true for your environment
          unless you are using the `webpack -w` or the webpack-dev-server.
       2. webpack has not yet re-run to reflect updates.
       3. You have misconfigured Webpacker's config/webpacker.yml file.
       4. Your webpack configuration is not creating a manifest.
       Your manifest contains:
       {
         "application.js": "/packs-test/js/application-5019ada8c79f4945bc85.js",
         "application.js.map": "/packs-test/js/application-5019ada8c79f4945bc85.js.map",
         "entrypoints": {
           "application": {
             "js": [
               "/packs-test/js/application-5019ada8c79f4945bc85.js"
             ],
             "js.map": [
               "/packs-test/js/application-5019ada8c79f4945bc85.js.map"
             ]
           }
         },
         "vendors~actioncable.js": "/packs-test/js/vendors~actioncable-111339b91a6898730a91.chunk.js",
         "vendors~actioncable.js.map": "/packs-test/js/vendors~actioncable-111339b91a6898730a91.chunk.js.map"
       }

And here's the output when I run bundle exec rails assets:precompile:

Sprockets::DoubleLinkError: Multiple files with the same output path cannot be linked ("tailwind.css")
In "/Users/.../app/assets/config/manifest.js" these files were linked:
  - /Users/.../app/assets/stylesheets/tailwind.css
  - /Users/.../app/assets/builds/tailwind.css

Does anyone have any ideas what might be the issue?