Generally speaking I feel like advice is kinda sketchy business because no two people’s walks are the same, what to speak of generationally — the world in which one generation grows up is different from the one the preceding generation grew up in. (This has always been true through every age, it’s worth remembering, no more so for any one generation. It’s always true.) There’s just a whole lot about life advice that I’m not into. Cooking advice I do, roast vegetables with oil and salt and pepper, do this thing often, they’re always a treat and are good cheap eats, good cheap eats are a lifelong joy. But “here, let me make a bunch of assumptions about your life and tell you what you ought to do with yours based on those assumptions,” this I avoid.
Having said that here’s an interesting thing about your question: you sound urgent to discover this niche, to begin your life. But speaking only for myself, I’ve inhabited a bunch of niches, and they were all interesting in some way, and they contributed to whoever I am now. I didn’t pick one at 21 and stay there. By no means! The Mountain Goats didn’t really start until I was 25. Even then, it didn’t become my main thing for another eight or ten years. So, “don’t be in a huge hurry” seems like pretty good general advice — that restless feeling of anxiety about not doing anything is self-judgment I think, but allowing oneself to just be where you are is one option you might always consider. Who knows — probably the world’s most successful people felt such a crushing need to always be moving forward that it inspired them to become wealthy, but being OK with wherever I’m at is, for me personally, a very important value.
Also whatever niche you end up in, understand that it’s fluid, not static, the idea that adulthood is about learning to stand still and rest on one’s prior experience is for sure one some adults adopt: some very sad, frustrated adults. I will never be done growing, always want to be getting better at being human, always want to be learning things, do not want to be settled into this niche or that, will never be satisfied to remember the good times. That’s just me and I will only be able to say if it was a good path on the last day of my life, which is not today, so I can’t really advise it, but I can say that it’s made for a pretty good day today.