@Kenso88 

Hi,  Did you install the Spotify APP on the Samsung S21 Ultra?

Except for the Sonos and Google Nest speakers, could the "Spotify Connect" find any other compatible devices, like your desktop?

Have you also tried the suggestions here:

https://support.spotify.com/us/article/spotify-connect/

Don't see your device?

• If you're seeing more than one device of the same name (e.g. iPhone), try connecting to each in turn.
• Try logging into the device using your Spotify credentials and you should be able to see it in the Spotify app even if it isn’t on the same WiFi.
• [Mobile] Switch off Show local devices only in the Spotify mobile app Settings > Devices. This lets the app see devices that currently aren’t on your WiFi network.
• [Web player] On the web player you can only use devices you’ve already logged into, or Google Cast devices on your current network (if using Chrome). If your device isn’t showing, try using the Spotify app instead.
• [iPhone] Make sure you provide Spotify access to your local network. Go to iPhone Settings > Spotify > Local Network, and toggle it on.

Thank you very much and best regards.

  @Kenso88 

Hi, Thank you very much for the time and patience.

The case has been forwarded to the engineer for further assistance. 

Please check the email for more suggestions.

Best regards.