Migrate a MyBB forum to Discourse

Needed to install some extra packages for the bundle install to run without errors in Ubuntu Mate 22.10 after following the Install Discourse for development using Docker guide:

sudo apt install ruby-bundler ruby-dev libpq-dev libmysqlclient-dev

However, there may be still something missing because when I try to run bundle exec rails db:drop it tells me Discourse requires Ruby 3.1 or above.
And ruby -v tells me I’m using ruby 3.0.4p208 (2022-04-12 revision 3fa771dded) [x86_64-linux-gnu].

So I think there’s something wrong with the guides or the scripts.