I'd say free will exists. Sure, you are shaped by your environment, your genetics and so on, but in the end you can still decide what you want to do. In theory I could simply quit my job tomorrow, wander off into the sunset and then drown in the next ocean. Or as someone brought up criminals, you could stab someone just trying to disprove the universe is being deterministic.

If you know every single atom in this moment and had unlimited computing power, you'd probably be fantastic at telling the weather. Or if you map every neuron in someone's brain you might know what they are about to do next. But at this point you are just looking at the present data and can maybe calculate the next few seconds (but not even that is 100% sure, just a very good guess).

The question is how far forward would you be able to look just based on current and past data? A minute? A day? A month? At that point the whole thing breaks apart in my opinion. It's like looking at the stock market where you have tons of past data and think you can predict the future simply based on that.

There's so many complex sources of randomness, the most likely solution is that things are just that, random. And you can decide what you want to do with your own life, at least until you die (or don't, who knows what the future brings). Honestly the whole question is dumb, there is no single being that knows everything, so it really doesn't matter. In the grand scheme of things even humanity is just a tiny blip on the timeline and we're with very high probability not unique. Just based on numbers there is a high chance other life forms have existed before us, might exist right now with us (somewhere else in the universe I mean, there's also plenty on Earth) and will exist in the future.