I had a lot of trouble casting to Chromecast Audio and Home from Desktop Opera WIN10 in recent versions of Opera and Chrome.
Usually spinner and then “no devices found”.
After troubleshooting with Google, it was confirmed that there was a systemwide issue with Chromium that was being patched.
Currently running Opera 60.0.3255.151 on WIN10-64 and cast works as normal.
Note that chrome://cast/#devices overview has been deprecated.
If cast box not showing test enable #views-cast-dialog in opera://flags/