Try things out as much as you can, and once you're good at something, that will "become" your passion or one of them, we tend to stick to things that we are good at.
Also don't be too hard on yourself, you're 20, you can't possibly have exhausted all the existing possibilities.
You only know what you know, so revisiting old things that you have tried, might also be a good approach as it takes time to develop the "taste/understanding" of a subject, sometimes researching "the best" of something and jumping straight there, you might not like it[1].
You might have learned from another field something that will change your perspective about a previous topic that you can put a spin on it; but again this is after you have understood "enough" rules so you can break them.
Picking something that is too challenging you might give up, and something that is not challenging enough, you might also give up, so pick something relatively challenging, but with a good headroom for you to keep exploring as you grow.
I used to jump from one "project" to another, so never finished anything, I decided now to prioritise 1 thing, and 1 thing only, it might take 5/10 years of my life, but what I decided was whatever I picked, I would exhaust "all" possibilities before "giving up", and my 1 thing is not giving up of it, and after a while I am actually enjoying.
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[1] from "Homo Deus" by Yuval Noah Harari p. 239-240.
Experiences and sensitivity build up one another in a never-ending cycle. I cannot experience anything if I have no sensitivity, and i cannot develop sensitivity unless I undergo a variety of experiences. Sensitivity is not an abstract aptitude that can be developed by reading books or listening to lectures. It is a practical skill that can ripen and mature only by applying it in practice.
Take tea, for example. I start by drinking very sweet ordinary tea while reading the morning paper. The tea is little more than an excuse for a sugar rush. One day I realize that between the sugar and the newspaper, I hardly taste the tea at all. So I reduce the amount of sugar, put the paper aside, close my eyes and focus on the tea itself. I begin to register its unique aroma and flavor. Soon I find myself experimenting with different teas, black and green, comparing their exquisite tangs and delicate bouquets. Within a few months, I drop the supermarket labels and buy my tea at Harrods. I develop a particular liking for 'Panda Dung tea' from the mountains of Yu'an in Sichuan province, made from the leaves of tea bushes fertilized by the dung of panda bears. That's how, one cup at a time, I hone my tea sensitivity and become a tea connoisseur. If in my early tea drinking days you had served me Panda Dung tea in Ming Dynasty porcelain goblet, I would have not appreciated it any more than builder's tea in a paper cup. You cannot experience something if you don't have the necessary sensitivity and you cannot develop your sensitivity except by undergoing a long string of experiences.
Good luck, and if you remember, let us know how it goes! =]