When you install Pixi using homebrew, it doesn't automatically update your path to include ~/.pixi/bin, which is necessary to make the global commands work.

You can manually update your ~/.zshrc to include ~/.pixi/bin in your PATH to invoke the pixi global command(s) from anywhere, or re-install using curl -fsSL https://pixi.sh/install.sh | zsh to have it do that for you automatically.