When you stand in a nether portal in the overworld and click on a bed to sleep in it, you will be transported to the exact location of your overworld portal in the nether.

For example, you can place your portal in the overworld at 200, 71, 200 and you will appear in the nether at 200, 71, 200.

I tested this and did it repeatedly until i reached 31999872, 71, 31999872

The glitch can be used to travel millions of blocks in the overworld, much like the old glitch where eating food in a portal would teleport you far away.

I have photographic proof of me at these coordinates, but unfortunately i don't think i can record it. You can test it out however, it should only take 10 minutes to make your way outside the world.

I couldn't find anybody else talking about this, and who knows how long its been in the game