I have no heat and the car is leaking coolant
You get your heat from the hot coolant from the engine (on a normal ICE vehicle) going through the heater core, when the coolant level is low from a leak, it can/will affect the function of the heater in the vehicle… Now there are many reasons a heater may not work, but since you also say you have a leak, then the 1st thing you need to do is find and repair the coolant leak and properly bleed all the air from the coolant, then there is a good chance the heat will once work again, if not then you will need to do a heater diagnostic… So, most likely you have one issue making it seem like 2, but you could also have 2 separate issues to take care of both.
Welcome to the forum…
Suggest to ask your shop to make sure there is enough coolant in the car’s cooling system to keep the engine within its temp specs. . There’s a possible risk of engine damage.
Note; I’m just a knucklehead diy’er with no experience with a 2018 H G. Just offering an opinion is all.