How do I publish a prebuilt plugin?

Our workflow involves publishing our plugin to an internal repository, where we then test it in its final state before we’re happy to release it in public.

I’m struggling to see how to fit this in with publishing to Gradle Plugin Portal, especially with the latest versions of org.gradle.plugin-publish which seem to do a lot of magic.

If I was going to upload a plugin post-build, is it purely a matter of doing a standard Maven-style upload of particular resources to a repository, or are there special proprietary things that only the org.gradle.plugin-publish plugin knows how to do?

That’s unclear as that plugin unfortunately is closed source.
But as far as I know it indeed is not a simple standard Maven-style publishing.
So you probably need to somehow configure the build so that it works with that plugin.