LIGO detects most massive black hole merger to date

My understanding is they just spiral into each other forever.

From our point of view nothing can actually fall into a black hole, instead it time dilates into nothing. "It is true that objects that encounter the event horizon of a black hole would appear “frozen” in time"[1]

So we would never actually see the black holes merge. In fact I'm not clear how a black hole can even form in the first place, since it would take an infinite amount of time to do so (again, from our POV).

(And yes, I know that from the POV of the falling object, they just fall in like normal. But that doesn't help us, because we'll never see it.)

[1] https://public.nrao.edu/ask/does-an-observer-see-objects-fro...

This is true, but it's not an observable distinction. It's true that in some sense those two black holes "haven't yet collided", but at this point they're well past the point of last observability and have now red shifted and time dilated into the invisible background. All the interesting stuff happens before that.