Unfortunately, kbin instances are unavailable via Lemmy right now due to hosting problems on kbin's side of the equation (see Kbin Codeberg #101). This will probably be fixed soon, so keep an eye on that issue for progress.

Even if it were working, however, there's actually something of a required ritual that you'll need to go through when subscribing to an external community which your instance is not already federated to (i.e.: communities where nobody on SDF is currently subscribed). Here are the steps you'll need to follow:

1. In the community search, paste in the following pattern: [!community@instance.domain](/c/community@instance.domain) (e.g.: [!technology@beehaw.org](/c/technology@beehaw.org))
2. Press [Enter], wait for the search to finish (it's normal to see no results)
3. Wait a few minutes
4. Refresh the search page and search for the common name this time (e.g.: "Technology")
5. The community should appear and be available for subscription now

FWIW: There are plans to improve this unintuitive workflow in the future (see Lemmy Backend Github #2951).

If these steps don't work, it's possible that the community may simply be too new. You'll sometimes need to wait an hour or so after a community has been created for it to start being available on external instances.