The web interface does not respect the setting where 'enter' sends a message (or not); pressing 'enter' does indeed send the message.
I have composed letters in Word (including line breaks) and then pasted the text into the web interface, but this is overkill.
So how does one create a line break in WhatsApp web?
Best Answer
You can press Shift+Enter to create line breaks in WhatsApp web:
I'm not sure if this is documented somewhere but many desktop applications and websites exhibit this behaviour as well; one of the examples is Stack Exchange's own chat server.