Matter to whom? Mattering to myself was an important step in my personal growth, and there are other people in my life who think I matter, and people I've never met who simply believe we all matter.

How sad to convince ourselves not to matter to ourselves by saying look, I don't matter to the universe, so how could I possibly matter? Does anything matter to the universe? If not, it's probably not the best entity to look to to figure out what matters. If the universe does care about something, who says it doesn't care about you, just because it's big and you're small in comparison?

Actually any choice we make creates a new unique timeline where different choice(like stepping on butterfly) will make radical changes in the future, diverging from mainstream timeline. As in Sci-fi time travel which changes the past a little, leading to enormous changes in future: this is the past, and we are shaping the future with our choices. Would it matter in far future if sun is destroyed, if we choose to invest in space expansion and colonize new systems? The future isn't set in stone, fatalism is just learned helplessness, robbing us of free will and drive to improve our condition.

I don't see how it's relevant. Things that will happen in 4 billion years have no bearing on my actions today.

Our experience is that many discoveries have changed the world and created a different future than that which we otherwise might have experienced. They would have had to be inevitable for them not to matter and that's certainly contentious though true in some cases. Given they have made a difference how does an extended time scale necessarily negate their influence? Your assertion might turn out to be true or not.