No sure where to ask about this, but here seems the most fitting... Is there a compiler plugin which allows to inline html/xml so we could write something similar like jsx/tsx?

I think thats not possible because compiler plugins can not change the syntax of the language.

Maybe we should do KSP (Kotlin Server Page)

Wouldn't Compose for Web fit your needs? It is not exactly HTML/XML but it is quite easy to use it like Jsx. If you can live without the < and > characters, that is. Also, there is the Kotlin/HTML DSL: https://kotlinlang.org/docs/typesafe-html-dsl.html

Yeah, but personally I don't like the dsls to write html if i could just write HTML

maybe https://youtrack.jetbrains.com/issue/KT-16366/Add-a-mechanism-to-hook-into-string-interpolation or https://youtrack.jetbrains.com/issue/KT-52924/Custom-string-literals