What you want is a Flink 1.x to Flink 2.x migration tool; that's much more complicated than simply migrating Kryo because there were lots of compatibility breaking changes beyond the Kryo upgrade.
Flink 1.x used Kryo by default everywhere. Flink 2.0 does not. That's a compatibility breaking change, and not Kryo v2->v5, it's Kryo v2 to non-Kryo. While the Flink 2.x codebase has tons of Kryo related code, and it's used heavily in unit tests and performance tests, I suspect a lot of that isn't used in production, or isn't used by default. Try running a local Flink instance, attaching a source debugger to Flink, and setting breakpoints in the Kryo code; it's not getting called in basic Flink applications.
