Given both kbin and lemmy are part of the fediverse, I would expect to be able to subscribe to https://kbin.social/m/tech by searching for [email protected] - but nothing shows up.
Which ones were piquing your interest? When I checked a few days ago, almost all the magazines with recent activity were "frontpage" topics like tech or news that are already well covered by Lemmy communities.
AFAIK because of the cloudflare check federation is now broken between kbin.social and the rest of the fediverse. Please somebody correct me if I'm wrong.
You are doing nothing wrong. Due to the load, kbin.social enabled Cloudflare protection which breaks their federating with other servers. Until they turn that off, they won't properly propagate to other servers.