wiki in update site metadata is optional. It's just that update-center2 always links to plugins.jenkins.io for public plugins, and lets that site deal with lack of documentation URLs.

https://github.com/jenkinsci/jenkins/blob/e4cba7380f25cff2b89edc951d84c8103994caac/core/src/main/java/hudson/PluginManager.java#L1472-L1476 means that there's an empty string as URL, resulting in a value-less href attribute (hbs), rather than no href attribute (Jelly). Firefox at least interprets this as a link to the current page.

It wasn't great before (there was still a hover state), but it's worse now.

Screenshots with a patched matrix-auth metadata, not having a wiki entry.