Jetpack Compose OverlayService. You have to have all the correct permissions granted and in your manifest, but if you do, this this will show a green box with "Hello" in it!

MyLifecycleOwner.kt

import android.os.Bundle
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleRegistry
import androidx.savedstate.SavedStateRegistry
import androidx.savedstate.SavedStateRegistryController
import androidx.savedstate.SavedStateRegistryOwner

internal class MyLifecycleOwner : SavedStateRegistryOwner {
    private var mLifecycleRegistry: LifecycleRegistry = LifecycleRegistry(this)
    private var mSavedStateRegistryController: SavedStateRegistryController = SavedStateRegistryController.create(this)

    /**
     * @return True if the Lifecycle has been initialized.
     */
    val isInitialized: Boolean
        get() = true

    override fun getLifecycle(): Lifecycle {
        return mLifecycleRegistry
    }

    fun setCurrentState(state: Lifecycle.State) {
        mLifecycleRegistry.currentState = state
    }

    fun handleLifecycleEvent(event: Lifecycle.Event) {
        mLifecycleRegistry.handleLifecycleEvent(event)
    }

    override fun getSavedStateRegistry(): SavedStateRegistry {
        return mSavedStateRegistryController.savedStateRegistry
    }

    fun performRestore(savedState: Bundle?) {
        mSavedStateRegistryController.performRestore(savedState)
    }

    fun performSave(outBundle: Bundle) {
        mSavedStateRegistryController.performSave(outBundle)
    }
}

OverlayService.kt

import android.app.AlertDialog
import android.app.Service
import android.content.Intent
import android.graphics.PixelFormat
import android.os.Build
import android.os.IBinder
import android.util.TypedValue
import android.view.Window
import android.view.WindowManager
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.wrapContentSize
import androidx.compose.material.Text
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.platform.ComposeView
import androidx.compose.ui.unit.sp
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.ViewModelStore
import androidx.lifecycle.ViewTreeLifecycleOwner
import androidx.lifecycle.ViewTreeViewModelStoreOwner
import androidx.savedstate.ViewTreeSavedStateRegistryOwner
import com.viatek.fitnation.echelon_android.R


class OverlayService : Service() {

    val windowManager get() = getSystemService(WINDOW_SERVICE) as WindowManager

    override fun onCreate() {
        super.onCreate()
        setTheme(R.style.ThemeOverlay_AppCompat_Light)
        showOverlay()
    }

    private fun showOverlay() {
        val layoutFlag: Int = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY
        } else {
            WindowManager.LayoutParams.TYPE_PHONE
        }

        val params = WindowManager.LayoutParams(
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.WRAP_CONTENT,
            layoutFlag,
            WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE or WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN or WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
            PixelFormat.TRANSLUCENT
        )

        val composeView = ComposeView(this)
        composeView.setContent {
            Text(
                text = "Hello",
                color = Color.Black,
                fontSize = 50.sp,
                modifier = Modifier
                    .wrapContentSize()
                    .background(Color.Green)
            )
        }

        // Trick The ComposeView into thinking we are tracking lifecycle
        val viewModelStore = ViewModelStore()
        val lifecycleOwner = MyLifecycleOwner()
        lifecycleOwner.performRestore(null)
        lifecycleOwner.handleLifecycleEvent(Lifecycle.Event.ON_CREATE)
        ViewTreeLifecycleOwner.set(composeView, lifecycleOwner)
        ViewTreeViewModelStoreOwner.set(composeView) { viewModelStore }
        ViewTreeSavedStateRegistryOwner.set(composeView, lifecycleOwner)

        windowManager.addView(composeView, params)
    }

    override fun onBind(intent: Intent): IBinder? {
        return null
    }
}

I have found a fix to the problem. Removing FLAG_NOT_TOUCHABLE and setting alpha of params to 1f did the job. Now the button or any other views/composables are receiving click events and also the transparency is removed. Also, Thanks to @tberghuis for his excellent Floating Timer open-source code.

Does anyone else get the error Class 'MyLifecycleOwner' is not abstract and does not implement abstract member public abstract val lifecycle: Lifecycle defined in androidx.savedstate.SavedStateRegistryOwner with lifecycle version 2.6.1?

I am facing the same problem with version 2.5.1. However, I have managed to resolve it by overriding the lifecycle as a variable instead of a function. Although the IDE is currently displaying an error ("lifecycle" overrides nothing), but the project can still be compiled and built without any issues.

override val lifecycle: Lifecycle get() = lifecycleRegistry

I also ran into this problem. Follow @AhmedMousa7 's method to solve this problem,

Android Studio prompts

Class 'LifecycleOwner' is not abstract and does not implement abstract member public abstract fun getLifecycle(): Lifecycle defined in androidx.savedstate.SavedStateRegistryOwner
'lifecycle' overrides nothing

but gradle compiles and runs without problems.

I found that the version of LifecycleOwner inherited by SavedStateRegistryOwner is wrong. The dependency it uses is androidx.lifecycle:lifecycle-common:2.0.0, not the expected 2.6.1. I suspect this is the reason.

Anyone else also using androidx.lifecycle:lifecycle-common:2.0.0?

There is an open source library to create overlay view with jetpackcompose
https://github.com/KuhakuPixel/UberAlles/

(DISCLAIMER: I am the author and still in early stage of development, would appreciate your feedback and fix :D )

@wilinz @FreePhoenix888 I fixed the ComposeView not recomposing by, in addition to lifecycleOwner.handleLifecycleEvent(Lifecycle.Event.ON_CREATE), adding

lifecycleOwner.handleLifecycleEvent(Lifecycle.Event.ON_START)
lifecycleOwner.handleLifecycleEvent(Lifecycle.Event.ON_RESUME)

Reached the same conclusions on some of the comments, specially the updated APIs and the requirement to trigger the START and RESUME lifecycle events so recomposition worked. I found the snippet here, that's why I was unable to find the updates suggested by commenters: https://www.jetpackcompose.app/snippets/OverlayService See my code here: https://github.com/xrubioj/JetpackComposeOverlayTest