What does kalpa actually mean in Buddhism?

I heard that in some suttas, it is mentioned that our world is destroyed by the heat of the sun, and that this heat rises up to the Brahma loka. Some Buddhists and Hindus believe that the deva lokas are located vertically upward in space from Earth, possibly millions of kilometers away. So according to these suttas, humans, animals, hell beings, and deva lokas will be burned, but the Ābhassara Brahma loka will not be destroyed. This seems to suggest that it is not the end of the entire universe. If we think in terms of our solar system, the Sun will become a red giant, and regions within about 200 million km may reach temperatures around 1000°C. So Earth would be destroyed in that process, and hell, animal, and human realms would also end and be burned. If we interpret that sutta as referring to the end of our solar system, then a kalpa might be around 10 billion years. Hindu scriptures describe a kalpa as about 4.2 billion years. Maybe I am wrong, but do the scriptures mention a kalpa as the lifespan of all lokadhātus, like the whole universe? However, my main confusion is that in Buddhist texts, a kalpa is sometimes described as an extremely long time period (by examples), even hundreds to thousands trillions years. Why are such extreme numbers given? If a kalpa means the lifespan of one whole universe, then how do Buddhist texts say that some Brahmas live for 64 kalpas? Where do they live during the next universes? Please do not treat this as a non-Buddhist argument. I am a Buddhist, but I have this question.