What is the current state of Box2D physics in Unreal Engine?

I searched a bit on the Web, and the latest reliable thing I found about Box2D was from 2014.

So: what is the current state? Is it still experimental? I can’t find any documentation about it.

What exactly happens when I check the “Enable 2D Physics” checkbox in my project settings? Will it use it? (The Tooltip says it CAN use it)

Will all objects that are simulated in any plane be simulated with 2D physics or do they have to use a specific constraint mode (like XYPlane)?

Will it simulate 3D Mesh assets that are constraint to XYPlane, or can it only simulate Paper2D sprites?

I’m looking forward to some answers!