if we got all the cats in the world to meow at exactly the same time how loud would it be
Well the average cat meow is like 65/75dB (above speaking volume but below shouting) and there are about 2bn cats in the world, so, by that math, 130-150bn dB. Which is about 100 million jets taking off at once.
Although dB increases logarithmically, not linearly. So it wouldn’t be quite as loud as that. But still quite loud, yes.