I've noticed that a lot of cultures have myths around the sun and moon. Specific examples including Inuit and Egyptian folklore refers to one chasing the other. I've wondered if references to celestial bodies might actually have been describing supernova.

Personally while I doubt I would have understood what the sun or moon actually were, given I was alive during an earlier period, I can't imagine the sun or the moon would inspire much intrigue or mysticism. They've been around for an incredibly long time and early humans would have been quite used to being unable to accurately or definitively explain their environment, but imagine if one day a star brighter than the moon appeared in the sky, clearly visible during the day and slowly faded over several months.

I could imagine that experience being passed down through oral tradition, with successive generations not experiencing similar events for hundreds or thousands of years due to the rarity of said events. Successive generations may have interpreted these stories as describing the sun and moon as a result, possibly even modifying them intentionally to better narrate their environment.

Related to your point about the devastation a relatively mild flood of today's standards could have had on our ancestors and how different cultures could generate similar flood mythos as a result, I think the same could have occurred in religions or folklore from attempts to describe a variety of different events.

It would make sense that if two distinct groups experienced a volcanic eruption, earthquake or tsunami even if they were separated by a large amount of time or space, could describe these events in similar ways. Also reminiscent of folklore similarities between supernatural entities, I believe many cultures describe a demon/creature/entity that would sneak into your home as you slept to drain your strength/power/life often alongside a feeling of being crushed or held down. Personally I've always thought this could be a way of describing sleep paralysis.