Streaming from Jellyfin to Chromecast

[Uberkeyser]

Thanks, Niels. But it does not explain the phenomenon. For complete disclosure: I am using Home Assistant to trigger a stream from KODI (DLNA/Upnp) to Chromecast. It works like a charm, as long the source is using a codec that Chromecast can handle so no transcoding necessary. But neither KODI nor Home Assistant is connected to a cloud (That's a fact not a guess)
As an explanation I was rather thinking of something like UPnP using neither domain names nor https, hence Chromecast's dendency on Google's DNS is irrelevant for Upnp. But then this should also apply to Jellyfin.