What is it that you’re then missing in the release notes?

I don't understand it indeed. That ticket talks about registering serializers that used to be without a specified registration ID, but now these serializers have been pinned

In what situations would a user be impacted by that?

Now i was not using Flink scala APIs. My transformation logic was written in scala internally and i bundled scala 2.12.7 with my application. But i was running into serialisation issues due to Kryo.

In this case, you have logic written in Scala

So you are not using Java types only, right?

In the release notes for 1.15, it explicitly states

If you only intend to use the Java APIs, with Java types, then you can opt-in to a Scala-free Flink by removing the flink-scala jar from the lib/ directory of the distribution.

Do you think it looks like the blog are the release notes?

I see. Because the release notes are at https://nightlies.apache.org/flink/flink-docs-release-1.17/release-notes/flink-1.15/

The Scala Free is a blog post only, to deep dive into some of the changes and the new capabilities it brings