Vegan crème brûlée would be an incredible challenge. Seriously. It's literally just heavy cream and egg yolks (and a touch of sugar). There's nothing non-vegan in the base recipe. And my wife can eat neither dairy nor eggs because of an autoimmune disease, and we've tried every substitute for both eggs and dairy. You might get the thickness of the cream from coconut milk, but then it tastes like coconut. And aquafava is a decent egg replacer and might give you the loft, but it's a better egg white replacer than egg yolk, and the recipe calls for yolks (you discard, or use the whites in something else). There's no good vegan replacement for yolks; it's a curse in baking. There are 80 million dairy replacers, some quite good, but eggs are still not there. Just is Ok for some uses, but not for baking.