When I worked at McDonald's years ago, the franchise location that employed me did have one or two microwaves in the back. They were used to warm up the burger before it was sent out. The microwaves were eventually removed and stricter quality control was enforced.
McDonald's meat is raw and frozen, and is stored in a refrigerated cooler near the grill. The grill has already been shown in this thread, but I wanted to add that it does also use a lot of pressure to squish the burgers, decreasing cooking time and keeping the burgers from becoming misshapen. After grilling the burgers, I was required to sprinkle seasoning on them. Those burgers, as well as all of McDonald's meats, were placed in a lined tray that was inserted into a custom warming slot. Each slot had a timer above it to track cook times, and when the timer went off, we were to throw the meat away. We rarely did. Additionally, there was a warming bay for prepared burgers available for the workers up front to access, and no burgers were supposed to sit in there for longer than 10 minutes. People noticed when we left them for too long (the burgers would dry out) so it was usually enforced.
Buns were toasted through a top-loading belt-fed toasting oven. The heating plates inside the oven were anti-stick coated, but the coating would burn off or get so covered in bun remnants that the buns would often exit a shredded, burned mess. Cleaning that was a chore and tended to be the thing that slowed down our orders. Maintenance of that oven tended to be a nuisance and dangerous, requiring us to either accept minor burns to swap out the anti-stick sheets quickly, or wait for it to cool before making the swap.
McDonald's also had contests across all its stores to seek out the best employees in every department, offering prizes and promotions to the winners. The winners would eventually be able to work for a bit in their main location--or maybe it was the test kitchen; I don't remember.
McDonald's food is often unhealthy, but there is a surprising amount of optimization and testing involved before the burger ever makes it to the franchise locations. It was a little unnerving to me at times, because I felt like I was working on a science experiment rather than a recipe.