Don’t get me wrong F# seems like a nice lang but definitely not mainstream (non geeks don’t use purely functional langs).
You can’t deny Kotlin is bigger lang than F# by any ranking from those popular (Tiobe) to unknown ones and is build on top of much bigger ecosystem (JVM) - that’s IMHO much more important factor for anyone doing commercial projects.
Additionally there is a big incentive to use it over Java (if you are stuck with older JDK) contrary to using F# over C#
Kotlin as a lang is better than C# (which is normal - it’s newer) and has better default IDE (IntelliJ) than anything on the market.
Well a bit exaggerated. Seen two Fortune 500 companies moving all never stuff to Kotlin on backend on my own eyes (for the reason I mentioned above) in some branches.
Spring supports anything that can bring them support contracts.
Kotlin, popular outside Android?
Reality check over here,
https://spectrum.ieee.org/the-top-programming-languages-2023