Coal is basically solidified crude oil -- decayed plant matter, compressed over long, geological time. For cooking purposes, burning coal differs from burning charcoal in that exposure to a coal fire can poison your food with petroleum by-products. Coal can be used to fire a stove or an oven, but only if the food is in a completely separate environment from the fire.
"Indirect heat" as in barbecue terminology is not indirect enough when the fuel is coal.
In coal-fired pizza ovens, which are still used in the Northeast US, and not to confuse them with wood-fired hearth ovens. A coal fire is much hotter than a wood fire and would be great for getting the thermal mass of a big ceramic oven up to temperature, but the firebox and exhaust are completely isolated from the cooking chamber.
Humphrey's Down East Beast, Weber Kettle, Kenmore Elite Gasser, Camp Chef Smoker, Camp Chef Denali