I recently purchased chromecast 2 and wanted to use it with Ubuntu 18.04. I searched here and saw all answers were from 2013 and nothing works. There is also an addon on chrome apps but that is old and discontinued. (Link)
Anyone here using chromecast 2 with ubuntu 18.04 ? This will be of great help
Casting from Chrome to Chromecast is now native function, you don't need any plugins. Just open options menu on the right and choose "Cast...". After click I can see both of my network Chromecasts (including Chromecast Audio).