> What blows my mind is that 20 million light years also means that what we're observing something that happened 20 million years ago.

Well... Not really. It took the entirety of the book A Brief History Of Time to even grasp a cusp of this, so I know I won't convince you in a short HN comment, but "now" is the collection of events that currently affect us. Due to causality, events outside our light cone have not occurred yet. They have no more influence than does an egg falling off the counter that has yet to hit the floor. The egg breaks only when it hits the floor - events only occur in our reference frame when they could affect outcomes in our reference frame. C is the propagation of causality, the fact that light travels at that speed in a vacuum doesn't affect that.