Dead battery after two weeks of travel, is it normal or is something draining it?

[simregistration]

I got back from a two week trip last night, and my 2019 Kia Sportage will not start at all. There was not even a click, only a dim light on the dashboard that went out in a few seconds. I parked the car in my building garage before I left, so it sat the whole time without moving. My father in law says batteries just go flat when a car sits that long. My neighbor says a healthy battery should survive two weeks easily, and that something in the car might be pulling power while it is off. I didn't know who to believe, so I read about it online. While searching I saw the name Car Jumpstart Pros come up, and I only opened it to see what a normal visit includes, like a battery test and a check for anything draining power. It made me think a jump start alone may not be enough. The car is only three years old, which makes me more confused. So I have some questions. How long can a car sit before the battery goes flat, and does it depend on the weather? How can I find out if something is draining the battery, like a light or a faulty part? Is it better to charge the battery fully with a charger after a jump start, or just drive around for a while? And should a three year old battery already be weak, or is that a sign something else is wrong? If you came home from a trip to a dead car, please tell me what the cause was and how you fixed it. Thanks a lot.