I’ve tried for some time to get casting to work after Google stopped the cast extension because it is now builtin inside chrome/chromium, so I looked around and found out how to enable casting to chromecast devices from inside chromium browser. To do so, simply paste this line in a browser tab:
chrome://flags/#load-media-router-component-extension
In my case the media router component was set to “default”, so I disabled the media router component, after doing so chromium will ask you to relaunch the browser, after it has loaded again enable the component again and relaunch the browser one more time. Now try casting and it should work, simple as that!!