In case someone wants to use the new interface: you can insert a line break without sending the message by using Shift+Enter, instead of just Enter.

Perfect. Thanks.

On the new interface, click the pen icon, then in the window that pops up, click "INFO" in the list along the top, and then click "Legacy Board".
For your interface to default to classical, from Home go into Settings in your Account and switch the Default map UI.
A different approach is to create your multi-paragraph message in a text editor, copy and paste the text into the graphic interface's message box to then send it.

On my computer, if I hit enter on the graphical interface, it sends the message.

I would be fine to use the classical interface if thats the only way to do it. How do I switch to the classical interface?

Eh? What do you mean?

Press doesn't auto-send when you press enter, or certainly not if you're using the Classic interface. Being able to type multiple paragraphs is normal. Then you press the "send" button.

Is there a way to turn off the "send" when hitting enter to allow multiple paragraphs in one message?