The overloading of return to either send a message or add a newline has become really annoying since chat apps (and then now AI) have become popular.

You have to keep a mental context of whether you need to hold shift before you press return. See also: every message I've ever sent that ended with I' because I fat-fingered the ' key while typing a contraction.

Terminal keyboards generally used to have two separate ENTER (submit the form to the mainframe) and RETURN (insert a line break) keys. I mean, even the original 101-key PC keyboard has them: the RETURN key above the right Shift, and the ENTER key of the numpad.

Shift+Enter will usually enter a newline in a message without triggering send... At least that's the convention used most of the time. No guarantees on specific applications, just my own experience with this.