thick stews/curries have some base ingredient which is the reason why they're thick.
If you're talking French food, you would start with a roux. That's butter and flour cooked in the bottom of the pan until it browns. Then the liquid is added while folding and stirring to try to minimize lumps.
If you're a American vegan punk, you might make your curry out of squash. boil or roast a butternut and huck it in a blender with some olive oil.
Others may use full fat yogurt, coconut milk, mashed tubers, mashed legumes, etc.
Powder mashed potatoes can be a quick fix maybe ?
And then there's cornstarch which I would view as more of a last resort or a final slight adjustment at the end.
A small amount of corn starch is added to a small cup. Cold water is mixed in until it's fairly homogenized and there's no lumps. And then the mixture is poured into the hot soup while stirring.
