Oh dear - you have started seeing the matrix!
Seriously, the truth is, you've got it right. There is no pre-defined 'purpose' to existence. One day, the sun will be a bit of charcoal, and that'll be the end.
With that established, you do have a whole life ahead of you that you're sort of stuck with. There isn't much to do except have a blast while it lasts! What else would make sense, after all.
There are a few restrictions, such as that you'll probably want to be sufficiently productive to sustain a lifestyle with healthcare, food, clothing and a safe place to sleep.
You have a lot going for you. You have the intelligence to figure out that there questions about existence that society doesn't really have an answer to. You have the wisdom and warmth to value friendship and family above other things. You are probably physically healthy too.
Kind, wise, and a bit too smart than is good for your mental health.
Now, a few practical steps...
First, lay off Reddit and the like. It's just the digital equivalent of alcohol: to be enjoyed in small doses, not too waste your days away. If you find out that skipping a few days is hard, then you have discovered how addictive these screens really are.
Second, much like advice already given, think of something you find cool, and look into that. Do check if it allows a lifestyle that you want.
This is hard.
Today I dreamt of walking into a local bank and saying: "let's stop foreclosing homes and making entire neighborhoods worthless. Let's just let these people keep their house, and work on their budget management skills and find a job for them. We'll issue a local iou-currency that costs us nothing, give micro-credits in it, and start building a local, small-scale community and economy. It's the only way to save them, and thereby, our bank." Unfortunately, it's a few years late for that one.
Or I imagine working on transport and neighborhoods, just making things nicer.
Or try to figure out rules that would lead to a cost-efficient health care system.
You say you have some financial freedom, maybe you can make a sufficiently profitable dream a reality.
If you manage, let me know how you did it. I'm still working on that part.
Third, do keep busy. You'll have less time to think about your existential crisis and you'll be more likely to come across something that you'll like, which would solve the whole thing. At least it beats being on Reddit the whole day.
Good luck.