So I started coding a custom camera in GDScript by modifying the viewport, since Camera2D seems to not work well with ParallaxLayers and zooming.
So, how is zooming actually accomplished behind the scenes?
Camera position, rotation and zooming are accomplished by scaling the canvas transform on the Viewport: http://docs.godotengine.org/en/3.0/classes/class_viewport.html?highlight=canvas_transform
However, I believe doing this manually will not solveParallaxLayer issues. Something about zoom has been reported already: https://github.com/godotengine/godot/issues/11555
So you may eventually roll your own parallax system (which I did in 2.1 heheh)
You got any example code how you wrote it?
FYI: I got it to work now by making a CanvasLayer's children following the "actor", not the viewport. Only thing that I struggle with is how to implement dragging and smoothing when using this approach...any idea?