so seems like

serializerByTypeToken

does not work on parameterized types because it passes the wildcardtype on to the next (recursive) call for my ktor PR i fixed it like so: https://github.com/NikkyAI/ktor/blob/2ace29d5478d6f51278b47934884858f17e78c00/ktor-client/ktor-client-features/ktor-client-json/ktor-client-json-jvm/src/io/ktor/client/features/json/serializer/SerialHelperJvm.kt#L24-L29 should i make a PR for this ?

Yes, why not

there you go https://github.com/Kotlin/kotlinx.serialization/pull/212