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Downgrading the Ruby version on macOS depends on how you installed Ruby. Did you use Homebrew or a version manager like asdf chruby, rbenv, or rvm? See Check Ruby version on Mac to check. If you're using the "system" Ruby don't uninstall it as it is there for macOS, not you. If you installed Ruby with Homebrew, it's best to install a software version manager so you can switch among Ruby versions. Asdf is good for managing multiple languages. Install Ruby with asdf if you are developing Rails web applications (which require Ruby, Node, and Yarn) or if you are using multiple languages such as Ruby, Node, and Python. Install Ruby with chruby, rbenv, or rvm if you need to manage only Ruby versions (chruby is simpler than rbenv or rvm). If you installed Ruby with a version manager, you can switch among versions. See Downgrade Ruby on Mac for details.