Thank you all you wonderful people for your advice.

I just discovered I face another problem, that I'd like to ask your
advice about.

Going along with the felt paper layering idea, I was playing around
with how things were going to look like, when I realized that if I
attempt to level the dip and then put my flooring on, the door to the
bedroom does not close anymore.

So now I'm sort of stuck. Do I level the floor and then put the
flooring on and then cut my hollow core door to size, or do I just
leave the dip and put the flooring on, in which case, the door with
close?

The wood flooring will run perpendicular to the door frame when
installed. The dip is app 3/16 inch at the door entrance.

Any advice is greatly appreciated.