I gave #Kbin another try, took a less popular instance without Cloudflare, create a magazine with appropriate tags in settings.
When I go and make a post on Mastodon with one of those tags AND even mention the group where magazine resides (just in case), but nothing makes the post appear on Kbin.
You can imagine my disappointment, as I promoted the shit out of Kbin prematurely and how it's suppoed to fetch remote posts - NOPE, doesn't work. 🤔 😔