Hole in a cube with boolean I have the same problem like this:
Boolean Issue: hole in mesh is.... strange

I need to cut a hole in a cube. I'm trying to use a Boolean modifier.

It doesn't cut but extrude actually a hole from the cube.

I'm in Blender 2.8. So there is no Solver option in Boolean modifier.

How is it better to cut a hole in a cube in 2.8?
I went through the manual and found that it is supposed to work that way. you can instead go to user preferences and tick the loop tool add-on.

then subdivide the surfaces -> select the faces you want -> edit on the side panel ->
loop tools drop-down -> click on circle -> later you may delete those faces.
Add more subdivisions if you want a more accurate circle or add a subdivision modifier(you might want to clean up a bit by adding edge-loops.