It never showed up in Software Update for me, so I redownloaded it from the STP website after deleting the old version and it's Library folder (username/Library/SafariTechnologyPreview) and restarting. A rework like this really will work best with a fresh start in terms of the .app and .plist files. It isn't like the prior several builds which aren't that different.
It has not been pulled. It works very very well. I'm not ready to do betas yet on my devices including that of macOS Monterey or even installing Safari Beta, so this is my way of trying some of these new technologies. I LOVE the new Safari! It's faster, cleaner, and seems to be more on par with what I expect from a Chromium browser which I also use. It has pulled me off of Microsoft Edge 91. I really feel like it's also better on YouTube. It just has less jank overall.