Sure @britzl …
In this page https://defold.com/manuals/android/, below the Creating a Keystore title there are a reference(link) to a forum post about creating the keystore. The post is this:
https://forum.defold.com/t/upcoming-change-to-the-android-build-pipeline/66084
That post talk about android application bundles and says that you need to create the jks file in order to sign your apps.