Blur toolbar background on Jetpack compose

In Jetpack Compose there is the Modifier.blur() method. But it blurs the content of the container it's applied on.

I have a similar structure like this:

Box {
    Toolbar()
    Content()
}

The Toolbar is above the Content in the z-axis. I want to give Toolbar some opacity and Blur everything from the Content that is behind the Toolbar.

How to achieve this?