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 -y build-essential bison zlib1g-dev libyaml-dev libssl-dev libgdbm-dev libreadline-dev libffi-devInstall:
Check .zshrc is sourceing /usr/local/share/chruby/chruby.sh and /usr/local/share/chruby/auto.sh for autoswitching. Restart terminals.
Start installing: ruby-install 3.1 installs the latest stable version of 3.1.
ruby-install heavily relies on hopping into sudo mid-install to satisfy dependencies.
I haven't been able to get this to install for a user without sudo access.
However, installing for a sudoer and then manually moving the .rubies/ruby-3.X.X directory to the non-sudoer user directory and sudo chown -R user.user /home/user/.rubies seems to work.