Hi! I am currently working on an aap with all composables (No fragment) with single activity, I am little confuse about navigation compose. If in future, I have to use fragment in this app, can I navigate from a composable to a fragment or How its work?

I don't think you'll ever need fragments again. Using fragments and compose together works as a migration strategy, but when you create apps from scratch, no fragments are needed. Navigation compose can't be used to navigate to fragments as far as i know.

What if you integrate 3rd party library that is still using Fragments?

Navigation can be used to navigate to any destination as long as there is a navigator for that type, so it's totally possible to navigate to a fragment. You can do something like this:

val navController = rememberNavController()
val activity = LocalContext.current as FragmentActivity
val fragmentNavigator = remember(activity) {
    FragmentNavigator(activity, activity.supportFragmentManager, R.id.containter)
}
navController.navigatorProvider += fragmentNavigator
NavHost(navController, startDestination) {
    addDestination(
        FragmentNavigator.Destination(provider[FragmentNavigator::class]).apply {
            route = "SomeFragment"
            setClassName(SomeFragment::class.java.name)
        }
    )
}

@Albert Chang How would you set up the Activity to support having a container and your composable next to each other?

That's what you need to figure out yourself depending on your use case.

Don't do any of this please. Your composable destination can inflate layouts that include fragments with

AndroidViewBinding

and they'll work just fine in Compose https://kotlinlang.slack.com/archives/CJLTWPH7S/p1621085039089800?thread_ts=1621026431.053700&cid=CJLTWPH7S