Is it possible mix 2d and 3d camera together?

I thought it bother a lot people and make confuse,
I have google a while for “make 2d and 3d scene together”,
many answer is use “render target with widget for 2D”,

the request is quite simple but why so hard to achieve?

The common way to do with my experience is,
first set projection with 3d camera then draw the things I need then change projection to 2d camera then draw the things,
but UE4 seems can not do this!?

Is any easy way to make a 3D scene and a 2D scene together(render target with widget is just too much work)?