I'm replacing my old over the range microware, which doesn't have an outside vent. I'm replacing with a new LG over the range microware LGV1680ST. It talks about installing
An outside vent. Do I really need to?

Almost all of the over the stove micros give you a couple of options;direct vent outside, which I prefer because of odor, and back vent to the room. Read your manual or on line info, it should work like your old one. If you have never done one before, be careful, they are heavy and you need 2 people. It most likely is mounted to a wall bracket and secured from the cabinet above it, look for screws or bolts there. Good luck