This video is a bit misleading.
Chromecast 4K only support E-AC-3 audio with Atmos, if you are trying to play TrueHD then it won't work now and there's a pretty good chance it never will. Chromecast because it technically supports Atmos, just only from E-AC-3 audio tracks. You will have to use another device with TrueHD Atmos support if you want to get Atmos from those tracks. Devices with TrueHD Atmos support includes: Nvidia shield tv, Xbox and a computer.
The Fire Stick 4K & 4K Max have always supported passthrough for DDP Atmos. Passthrough for TrueHD has never been supported. TrueHD will be transcoded by Plex Media Server to another format. The Cube v3 supports passthrough for both TrueHD Atmos and DDP Atmos. AFAIK, it is the only Amazon Fire device to do so.