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kotlinlang

do we have official viewmodel library by jetbrains for compose-multiplatform app, if no, what is the alternative ?

Yes viewmodel available multi-platform project 
<https://kotlinlang.slack.com/archives/C0BJ0GTE2|https://kotlinlang.slack.com/archives/C0BJ0GTE2>
<https://kotlinlang.slack.com/archives/C0BJ0GTE2/p1726154031208999|/p1726154031208999>

koin is not compulsory, correct ?

also, the viewmodel library is androidx and not org.jetbrains one

I think both are the same it. I am not sure about the viewmodel prefect iOS or desktop because I window laptop so not check it

Did you look at the official documentation? <https://www.jetbrains.com/help/kotlin-multiplatform-dev/compose-viewmodel.html>