I'm trying to display some text in the player's action bar:

player.displayClientMessage(SomeComponent, true);

But I'm having trouble creating a newline (that would create two lines of text).

I tried this, but it doesn't work:

Component.literal("\n")

Anyone have any idea how to do this?

the method displayClientMessage itself outputs only one line

you can write your own method for displaying such messages, for example using an overlay.

or try overriding the display ClientMessage method so that it accepts and processes List<Component>

in my opinion, your own implementation through an overlay will be the simplest way