ruby bundle - no config files

I've been attempting to try ruby on rails.

1. I installed ruby: sudo apt-get install ruby-full
   • this gave me ruby 2.7.something
2. the rails intro says I need ruby 3.? so I deleted ruby:
   • sudo apt uninstall ruby-full, I think
   • this removed ruby-full but ruby 2.7.? remained
   • I rm'd ruby
3. sudo snap install ruby --classic
   • ruby 3.? installed but at a completely different location

I have installed rails and got it running however I am unable to work with gems if I need to install another gem.

I have tried installing menu_maker but it isn't found when I try and use it.gem commands do not find menu_maker (an example gem, not a problem with menu_maker!)I can see that menu_maker exists at ~/.gem/gems

bundle config shows nothing. I do not have a config file, neither at <project>/.bundle/config nor at ~/.bundle/config

I don't seem to have environment variables GEM_HOME and GEM_PATH set either.

I assume there's quite a bit gone wrong here. My question is how to get the configuration set up, that's the environment variables and the config file? And anything else you can see will be needed!

I did delete stuff when removing ruby 2.7.? but I installed ruby 3.? after that.

I'm running Ubuntu 20.04.6 LTS