Yes, you can play lossless Dolby TrueHD/Dolby Atmos music on Blu-ray disc with an Arc + Sub + Era 300s setup. You just need a TV equipped with HDMI eARC and a Blu-ray player. Any model Blu-ray player will work. You can even use the Blu-ray player in a PS5 or Xbox Series X. If you have a 4K TV, look for a 4K UHD Blu-ray player.
Just know that there isn’t a lot of music available in Dolby Atmos on physical media. And when it is available, it often is only included with a “deluxe edition” box set which can oftentimes be very expensive. The Atmos Blu-ray disc of Pink Floyd’s The Dark Side of the Moon is a good example. It is only included in their 50th anniversary deluxe box set that costs around $300.
The next best option is playing Dolby Atmos music from Apple Music on an Apple TV 4K. The quality is not as good as Blu-ray but very comparable and more affordable with the best selection of music available in Atmos. IMO, the audio quality of Atmos music from the Apple TV is better than playing Atmos music directly from the Sonos app.