Yes, our stack is Spring Boot + Kotlin on the back side, TypeScript + Vuejs on the front. We’ve millions of unique visitors each month, and we’re pretty satisfied with the stack.

Cash App uses Kotlin Multiplatform, including server-side code, https://kotlinlang.org/lp/mobile/case-studies/cash-app

Google, Amazon, hundreds of F 500's

Absolutely. Kotlin is *widely* used for backend code at Amazon.

Yes