The works of Roger Penrose have shown that it's conceivable or potentially even provable that at the very largest scales of time and space, there is no meaningful difference between the accelerating "cold" end of our universe and the collossal expansion that began the universe as we know it, and in fact those two states are perpetually cycling, birthing new universes from the explosion of old ones. This is based on the idea that when there is no more physical mass in the universe, you can look at the universe from a reference frame that only looks at the geometry of the energy expanding through space and it's identical to the beginning states.

I would recommend PBS Spacetime youtube channel for a lot better explanations of conformal cyclic cosmology than my feeble mind can try to relate.

Maybe there were other big bangs, but we need evidence of that, and that evidence doesn't exist.

Jyst saying "but we don't know" isn't a replacement for evidence.