Ruby

ruby is keg-only, which means it was not symlinked into

/opt/homebrew

because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.

If you need to have ruby first in your PATH, run:

echo 'export PATH="/opt/homebrew/opt/ruby/bin:$PATH"' >> ~/.zshrc

For compilers to find ruby you may need to set:

export LDFLAGS="-L/opt/homebrew/opt/ruby/lib"
export CPPFLAGS="-I/opt/homebrew/opt/ruby/include"