How to run a completablefuture

Hi,
I'm programming a xamarin.android android app with ARCore and SceneForm.

I'm trying to translate to c# the code in arcore developers guide ar/develop/java/sceneform/samples , section create runtime simple shapes. More specifically this:
MaterialFactory.makeOpaqueWithColor(this, new Color(android.graphics.Color.RED))
.thenAccept(
material -> {
redSphereRenderable =
ShapeFactory.makeSphere(0.1f, new Vector3(0.0f, 0.15f, 0.0f), material); });

I've tried somethings that I managed to run, but then I get thread errors. Also I couldn't figure out what to put inside .ThenAccept().

In the xamarin github repo, the project sceneform has a sample that uses viewRenderable.builder().build() and it has two versions, one with completablefuture and another that takes a c# action. How was this done?

Is it possible to use/call completableFutures in c# ? How?

Please, any help will be very much appreciated. I already had to convert this project from xamarin.forms to xamarin.android, I would rather not restart it again in android studio.