Hi Miralem Zeljo, this works in ArcGIS API 4.x related products - Support Multi-Line Labels Using Arcade in AGOL
But, if you are using ArcGIS API 3.x apps (e.g. Operations Dashboard) - this functionality wouldn't work - as stated in the Arcade Documentation.
An interim solution would be to - pass a HTML tag for line breaks instead - <br />
For example:
{expression/expr0} + "<br />" + {expression/expr1}
This will cause any 4.x - apps and maps to look horrible, but will do the trick for 3.x related products (only works with popups not labels).