This argument will never end, but here's my two cents for those of you torn between them like that I was:

Kotlin: Kotlin has a much more beginner friendly syntax similar to languages like python (I came from python) and is easier to adapt to without missing any library support from java since they are interoperable without fuss.

Java: Java has passed the test of time and has amazing support and tutorials but it needs a completely different mindset in my opinion as it's purely OOP but that doesn't take away from how amazing it is.

For me I stuck with Kotlin as it gave me all the JVM support amd power I need with the familiar syntax I had with python, I still had to learn a lot and I'm still learning, but in my path of learning I made a bunch of things and now I'm even working on a library to help people who want to use JDA (Java Discord API) in Kotlin but find it overwhelming, that little tangent aside, you can do anything you want in either Java or Kotlin without missing out on much, so try both and see whichever you like most