@donallen in your original post you indicated “I got the same error on (…) a Mac running Catalina”, where by “same error” you meant Webpacker::Manifest::MissingEntryError. As this refers to a step occurring after installing/checking your ruby/node/yarn/rails dependencies, I had inferred that you got these installed correctly on your mac. FYI I run macOS Big Sur 11.1 but this should AFAIK not matter directly.
Anyways it appears to me the front-end compilation issue is caused by Node 15 being used although a fresh Rails install will resolve node-sass to 4.14.1 (this is not visible in the logs you provided but I can observe it in my fresh rails new blog install), which to my understanding is not compatible with Node 15. (NB: This is in the case of a fresh rails new install, where @rails/webpacker should resolve to 5.2.1, but as you had been modifying this dependency in earlier comments please double-check that you indeed have the version 5.2.1 installed—or better, restart from rails new blog in a new directory just to be sure.)
Therefore brew uninstall node && brew install node@14 or something of that sort would solve your issues, could you try that?
If confirmed it would indeed be good to update the getting started guide to indicate Node 14 is required, or at least instructing the user to check for their compatibility. An even better fix would be to enforce/check this compatibility by specifying the required Node version in the app itself (similar to the line ruby present in Gemfile), but I don’t know how that’s done as front-end is not by strong suit.
I get your point that getting started is not that easy, but from my experience, it gets better and I find Rails to be an amazing framework. The more I use it and the more I feel like sticking with it, whereas I can’t say as much about some other technologies. There is also some hope that front-end dev could get easier or more integrated based on some comments of DHH.
PS: as you are just getting started, now could also be a good time to start straight away with Ruby 3 which just came out.