7:46 The reason you can do it below y=0 is because it teleports you to the exact same coords in the end as you were in the overworld. This means that if you do it below y=0, it will teleport you into the void. It still works but is unusable.
idea: you could ask a designer to make a blue penguin end screen for your videos bc sometimes the end of your vids is hard to see bc the video sugestions cover it