A couple of years ago the limit was 1800 characters per answer, now it's down to 1200. The comments limit allows a little more than that and I think the mobile app also allows more (but who'd want to type that much on an iPhone?)
Seriously, you can fit a great deal into 1200 characters, especially when you edit out all the repetitions and circumlocutions.
Hello asker2400 I do not know the answer, but you can put as much as will fit into the More Details area of the question. This probably has to do with the fact that many of our users are on mobile devices and reading huge amount of text may be hard for them on a phone.