I have a Roku 4k Ultra device. But I don’t know if it has support for Dolby Atmos.
How can I find out ?
I don’t have the box or instructions any more.
Over the years there have been several Ultra models, all supporting 4K. What is your model number? Roku menu path Settings / System / About will tell you.
I tend to use the chart from https://en.wikipedia.org/wiki/Roku
While my Roku 4660 isn't officially listed, when I watch a movie from Apple TV+ or HBOMax, my Onkyo TX-NR646 receiver will display the input as Dolby D+ Atmos and output is 5.1.2. The Roku is connected via HDMI cable only.
I have a Roku Ultra-1 ( Model 4670x )
Per this Wikimedia chart, the first Ultra listed with Dolby Atmos support was model 4661, released in September 2018. All later models (higher model numbers) are listed as having Dolby Atmos support.