Since I wanted to verify whether or not Spatial Audio works on the Apple TV HD (non-4k) and did not find any answer, I tried it myself. So: Current state (tvOS 15 Beta 1) is that Spatial Audio does work on Apple TV 4K, but does not work on the Apple TV HD. I set up the beta on a 4K and a HD, and while the option is offered in the AirPods settings on the 4K version, it is not on the HD.
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