Let's look into what v4 offers and how you can upgrade your local install today. But after that, development on Valet slowed; as Taylor has often pointed out, "at that point, Valet was feature complete."
Upgrades to ngrok: If you use ngrok to share your sites, older versions of Valet bundled ngrok as an install.
If you're upgrading from Valet 3, here's my preferred way to upgrade: Edit your ~/.composer/composer.json file and update your Valet requirement to "^4.0"
Make sure you run valet install, as it'll check your system's compatibility and upgrade some configuration files for you.