RVM

Although this is not really a requirement, this is what I use personally to manage Ruby installations on my system.
RVM is a Ruby version manager, it installs and manage different Ruby versions in the system. It is installed locally in the home directory so it doesn't require a super user privilege.

Installation

curl -L get.rvm.io > rvm-install
bash < ./rvm-install

For bash completion add to .bashrc:

# RVM bash completion
[[ -r "$HOME/.rvm/scripts/completion" ]] && source "$HOME/.rvm/scripts/completion"

If necessary in $HOME/.rvm/scripts/completion replace line 22 with:

source "$HOME/.rvm/scripts/extras/completion.bash"

Set the terminal as login terminal in preferences.

In VSCode add to settings.json:

"terminal.integrated.shellArgs.linux": [ "-l" ]

Install Ruby

$ rvm install 2.7.1
$ rvm use 2.7.1 --default

Source: https://wiki.archlinux.org/index.php/RVM