Also found those links who may be interesting, especially the first one:

• https://kotlinlang.org/docs/kotlin-evolution.html#dealing-with-compiler-bugs
• https://discuss.kotlinlang.org/t/kotlin-support-roadmap/11454
• https://discuss.kotlinlang.org/t/commercial-support-for-kotlin-language/13359

https://kotlinlang.org/docs/security.html says:

Always use the latest Kotlin release.

It's still unclear, see #2073, #562, #1309