Hello. My root gradle project consists of two gradle subprojects- the backend (jvm) and the frontend (js gradle plugin). I want to extract the duplicate code for the data classes from both projects into some sort of a common module, so that I can share the data classes. Is there an easy way to share the code without creating a multiplatform project?

You can make just the common module a multiplatform project. Unless you just don't want to touch multiplatform at all.