I don’t know if there’s a true separation, as they’re fuzzy categories. (Ie, the edge isn’t a hard separation)
They’re both applications of dry heat, but baking typically assumes it’s in a relatively contained vessel (an oven, which may have a door or other way to access it that doesn’t close).
Roasting can be done over a fire, such as a rotisserie, in a fairly open environment. (It’s also worth noting that a ‘pot roast’ is braised, not roasted, as ‘roast’ also refers to a large hunk of meat)
Roasting implies high heat. It’s never done over low heat. As such it usually implies browning the surface of the food.
Baking tends to be a more controlled heat. The vessel mentioned earlier tends to be clay, metal, or other material with thermal mass so that the heat being applied can remain constant.
Roasting tends to have a high proportion of radiant heat, while baking tends to be more heat from the air (either conductive or convective)
Roasting implies fat to some degree, but it might be coated in fat or oil (such as potatoes), or just a hunk of meat dripping its own fat as it renders. But you can also brush butter onto bread before baking, so this isn’t a clear boundary.
Roasting also tends to be more hands-on. You have to baste, or flip or stir items while it’s cooking.
Baking usually implies that something is cooked all the way through. Although there are dishes that intentionally aren’t (such as ‘lava cakes’), we have expressions such as ‘half-baked’ to describe things that weren’t done correctly. Roasting can brown the outside of vegetables while leaving it crisp in the middle, or cook meat to medium rare.
… and then we get into the even fuzzier issues.
People often assume that baking a batter or dough being cooked (cakes, breads, cookies, or what we collectively call ‘baked goods’, although that category also includes pies and things that may be filled or otherwise processed after baking). And this potentially includes techniques that are closer to roasting (such as a creme brûlée, broiling a meringue)
So… baked Alaska is roasted, not baked.
I’m not sure if naan is baked or roasted. And I would say that campfire bread (wrapped around a stick, then cooked near the fire) is roasted.