School unfortunately does a pretty bad job preparing folks for what comes after. You go from a strictly regulated lifestyle where you are given very little freedom to a lifestyle you have to construct on your own.
The best way to figure things out is to give it a try. Maybe you saw a flyer for a trivia night and that vaguely interests you? Give it a try. Did a video about making a ship in a bottle catch your eye? Give it a try. Did you see someone having a really good time riding a skateboard and idly wonder if it'd be fun? Give it a try.
You shouldn't feel bad on trying stuff and not continuing with them after a bit. That just means you weren't really into that thing as much as you thought you might be.
A lot of the stuff you try might not be for you. I found out that I hate trivia at bars through personal experience. But that's ok, cuz I also found out I love karaoke at bars when the karaoke crowd came in after trivia. You'll meet people you like. You'll meet people you dislike. You'll meet people you are largely ambivalent about. It might take awhile, but you should only move at your own pace. Don't worry about other people and stay focused on yourself.
Something important to learn is that you should not be defined by your job. Your job is just something you do to pay the bills. If you are lucky, you'll have a job that you like and is personally fulfilling, but that's pretty rare in this day and age. You are much more likely to find happiness and fulfillment outside your job.
Try to enjoy the little things in life. I have been trying to make the perfect breakfast for a few years now as a way to get myself to enjoy waking up in the morning. Stack up your little joys and hopefully, you'll have enough joy for the entire day. Maybe even enough joy to share with others.
Much like exercise, there's no real shortcut to self-actualization. You'll need to do a lot of experimentation to find what you like an enjoy. I would recommend finding a consumptive hobby and a constructive hobby. You most likely already have tried a bunch of consumptive hobbies, as our society encourages consumption. If you haven't I would highly recommend experimenting with constructive hobbies, where you make stuff. It doesn't have to be drawing art, it can be stuff like working with wood, assembling models, writing reviews to bad movies. Anything where you add something to the world that didn't exist before. Consumptive hobbies I enjoy are reading books and eating cookies. Constructive hobbies I enjoy are making linoprints and baking cookies.
Your fears and doubts are ones that countless humans have experienced. They overcame those doubts and I'm sure you can too. You are not alone in your struggles and if things ever get too tough, there are always people willing to lend you a hand.
Good luck, buddy.