Thats funny because I thought it was shift-enter that creates a newline in a field where an enter submits. Just shows the fractured nature of this whole thing.
This is my thinking. Ctrl-Enter is usually "submit the form this input is a part of" in my experience, especially if you're in a multilinear text input (or textarea).
I've seen Enter, Shift-Enter, Ctrl-Enter, and Alt-Enter, (and on macOS, Cmd-Enter and Option-Enter), depending on the application. Total circus. I think this is actually a weakness of the standard keyboard: Keyboards should at the very least separate "submit form / enter" from "newline / carriage return" with different physical keys, but good luck changing that one, given the strong legacy of combining these functions.
It even works inside bullet points to add separate lines as part of the same bullet.