But something must have triggered the big bang.

That’s a separate claim you’d have to prove. We have no evidence of something triggering it, we don’t even know that it would need to be triggered. All of our observations occur inside this universe, therefore we have no idea at all if cause-and-effect even applies to the universe as a whole. The short answer is: we don’t know and have no reason to posit the need for something else.

What does it mean for something to be “beyond” everywhere or before time?

That’s a philosophical question, not a scientific one, since it’s by definition beyond the ability of science to answer. It suffers from the infinite regress problem which many people invoke God to solve (the uncaused cause) but that’s not very satisfying, is it?

Obviously God did it. /s