We are using Kotlin with SpringBoot + Hibernate + Redisson. Have no complaints whatsoever on stack, the only drawback I am experiencing is backend people have never seen/used Kotlin before so the initial friction and dogma of it's too complicated. Our Android apps do use Kotlin but there is nothing common from codebase being shared what so ever. I would still choose Kotlin but probably different framework stack not because I didn't like SpringBoot but due to projects like Ktor getting mature.