Not on Zero W or Zero 2 W at this time, and from what I've heard, they intend to add it to Imager so you can pre-configure it when flashing the OS, but not sure when. They would also need to have the package installed in the default OS image before doing that, too.
Yes; in my blog post and in the docs, the headless setup method is mentioned. Assuming you have a GUI-enabled installation of Pi OS, you can SSH into the Pi and install rpi-connect, then run:
rpi-connect signin
This will give you a URL to copy and paste into a browser. Authenticate with your Pi ID, and then the Pi will be connected.