Major domains where Kotlin knowledge can be used

I graduated couple of months ago from my college. Last semester of college I spent quite a bit of time on a project for Android Development in Kotlin. Now after graduation I joined the company where I got the job. I am part of the backend team developing on spring java. And now I realize my kotlin knowledge will soon go obsolete. But I want to keep in touch with it. In college I used to do competitive programming in C++. I still do but I now use kotlin. Better to keep in touch with kotlin rather than C++. I want to know what else areas can be explored in backend(not ui/appd) where kotlin knowledge can be used. I have extensive knowledge of coroutines too which I loved so much and now really forgetting those. Hoping to pick some side projects with kotlin.