Is all this bunker-building a sign the 1% know something we don’t
No.
and are preparing for end times?
Yes.
They fantasize constantly about their wealth becoming even more disproportionate to the general population - even if it, in absolute numbers, collapses. They crave more power over people, and are deluded enough to think that in a crisis scenario, their wealth will mean anything.
It's cute that they think the society that supports them is going to continue to support them in their bunker and they only have to worry about attacks. What are they going to do when the plumbing breaks or the canned food runs out?
Is it? Is it? Short of an utter and complete societal collapse the likes of which we have basically never seen, history tells us the billionaires will emerge from any catastrophe with even greater wealth.
During WWII the Nazis got their factories bombed to smithereens. Entire cities like Dresden got essentially wiped off the map. Can you guess what happened to the rich industrialists who benefitted from slave labor? That's right, they came out of their bunkers and proceeded to become richer than ever and are still household names to this day. Oh, and of course while everyone was on food stamps/rations the rich were having lavish banquets.
Capital is power, by definition. Instead of hoping for an apocalypse so bad all capital vanishes and even gold and land don't hold any value, maybe we should focus on wealth distribution through democratic means.