ah yes, so honestly i've figured this all out with my own testing, basically, before i type further, cover the telephoto camera, zoom into a light, uncover the telephoto camera, and watch as it actually (most of the time) switches, bear in mind it may not do this perfectly sometimes if your trying this but it will happen in most cases, basically to explain what's happening and why, its actually simply complicated, it is very simple to explain and understand but kind of complicated on a physical level (ish), basically the iPhone 11 pro camera's aren't all the same sensors and set ups but just different lenses or something, they're all different, and actually in fact you'll notice that the ultrawide angle camera and the wide angle camera (normal one) visibly looks different, look at brown carpet or something with the normal camera and then switch to the ultrawide, it'll (probably) look fuzzier on the ultrawide, that is for many reasons, one, its a 5 element lens instead of 6, two, f/2.4 aperture rather than a 1.8 or 2.0, and also not to mention, i found this out with research, the ultrawide camera's focus type is WAY different then the other two cameras (sadly in a bad way but luckily the fact that it's so wide covers up for it), and basically the ultimate question to all of this is, why? and the big answer is, this thing your experiencing is because the phone detects that the camera is pitch black so it switches to the wide angle lens and uses digital zoom because the wide angle camera is f1.8 and the telephoto is f2.0 and the smaller the f number, the more light gets let in, and it basically tries to counter the dark by switching to a camera that accepts more light, this has actually been around since apple released their first phone with two different cameras, the iphone 7 plus,
TL;DR, the iPhone 11 pro's wide angle camera and telephoto camera both have different apertures, the wide angle camera is f1.8 and the telephoto is f2.0, the smaller the f number, the more light that can be let in (aka the smaller the number, the better it is for the dark), since the wide angle camera has a smaller f number, it lets in more light, it notices the telephoto camera is pitch black (or atleast dark), it stays on the wide camera because if anything, since it has a smaller f number, either way it'd be the better option if it dark, so even if it doesn't help any, it'll stay on the wide camera just because its better than the telephoto, i hope you can properly understand this and that this helps and also yes, this is an example of apple's AI analyzing things and choosing what's best based on lighting, i hope this helps and honestly if you have any other questions, comments, literally anything, feel free to ask/say more and i or someone else would love to help more (also just for an ultimate answer for something, no, your phone is not broken, this is normal)