Install Ubuntu ruby prerequisites, otherwise you will be asked to use sudo even for a user install (though you can/may have to force ruby-install to skip dependencies with –no-install-deps):

• sudo apt install build-essential libssl-dev

Install:

• chruby
• ruby-install

Check .zshrc is sourceing /usr/local/share/chruby/chruby.sh. Restart terminals.

Start installing: ruby-install 3.1 installs the latest stable version of 3.1.