Read-only file system when attempting mkdir /data/db on Mac

Question

I am trying to create a new folder in the main directory

Tried all kinds of examples

sudo mkdir /data/db

sudo mkdir -p /data/db<

Answer 1

I am at a loss why Apple did that.. So now, we can not have any root level directory other than theirs ? This just doesn't make any sense and people creating with root privileges those folders know what they are doing