I see that note, and the wording on it confuses me. My recollection, and some confirmation from this article [1], is that I was using handyPrint when connected to the mac via USB. At the time of the blog post I wrote, I was switching from usb to ethernet, and discovering that I didn’t need a separate computer to make the bonjour / mDNS announcements.
It’s still reliant on the printer handling the correct print protocols (so that CUPS isn’t needed to translate), but my specific printer did work.
https://www.macworld.com/article/673717/how-to-add-airprint-...