Related reading: Preparations for Rails 7.1 ; the TL;DR version is that Rails 7.1 will also be producing Dockerfiles that can be used, I’m working with DHH to ensure that they are suitable; and I’m also working on a gem which can be used to regenerate the Dockerfiles on demand as your app changes.
Separately, I have started a draft of documentation introducing Dockerfiles to Rails developers. What you will find is that Dockerfiles are easy, but what you are doing is scripting what is likely an unfamiliar operating system, typically Debian, and that is where the learning curve.
Oh, and as to volta, you may be familiar with Ruby version managers like rvm or rbenv. Volta is that, but for node.js. It can be used to install the exact version of node and yarn that you use for development.