Unfortunately, Samsung TVs with eARC are known to have connection issues with the Arc. Although not ideal, disabling eARC on the TV seems to fix the problem for most people. This option probably won’t allow you to get Dolby Atmos audio from the Xbox though. But you should still be able to get Dolby Atmos audio from the TV’s native apps even with eARC disabled.

Here’s a thread with other Samsung users that have experienced eARC problems:

Thank you for getting back to me, and this is still happening? It’s been over a year since that thread was created? Maybe if I get something to connect my Sonos to and completed skip my Samsung Q90 maybe that might get it work without the cutting? It sounds like it’s on Samsungs side and not Sonos? 

The HDFury Arcana has seemed to work for some Samsung users, but it will only affect your Xbox and not your TV’s native apps.

Try this:

Make sure the TV has the latest software update. Then disconnect everything from the TV including the Arc. Unplug the TV and Arc from power for a couple of minutes. Plug them back in but keep everything disconnected. Make sure Anynet+ is enabled in your TV settings. Run TV Setup in the Sonos app. When the app instructs you to, connect the Arc to the TV’s HDMI ARC/eARC port using the Sonos-suppled HDMI cable. When the Arc has been successfully connected, connect the Xbox to the TV and test again.