With tvOS 14.2, which is currently in beta, Apple TV 4K has gained support for wireless game audio with HomePods – and possibly other AirPlay 2 and HomeKit compatible speaker systems.
Wireless game audio
The upcoming release of tvOS 14.2 for Apple TV 4K and HomePod is shaping up to be a big update. With the new software, the original HomePod will gain Dolby Atmos and 7.1/5.1 support, permanent Apple TV pairing, and something called 'Home Theater with Apple TV 4K'.
FlatpanelsHD can now confirm (thanks for the tip, Henry!) that tvOS 14.2 also brings support for wireless game audio to Apple TV 4K and HomePod. After pairing HomePod (or two HomePods) with Apple TV 4K, you can enjoy game audio from Apple Arcade games as well as games from the App Store.

Arcade's 'Sayonara Wild Hearts' game audio playing wirelessly on 2x HomePods
Previously, Apple TV's wireless audio output to AirPlay 2 compatible speakers worked only with video.
Wireless game audio requires the latest tvOS 14.2 beta 3. If you are experiencing minor audio delay, you can calibrate audio sync via the built-in 'Wireless Audio Sync' feature on Apple TV 4K. Remember that sync must be calibrated for each combination of resolution, frame rate, and dynamic range (4K60 SDR, 4K60 HDR10, 4K60 DV etc.)
Also read: HomePod gains 'Home Theater', Atmos & permanent Apple TV pairing
It may also work with other AirPlay 2 speakers but it will most likely require HomeKit support too. Currently, you must have Apple TV 4K and HomePod set to the same room in the 'Home' app on iPhone/iPad, and then group together the devices after which the two device icons will merge into one.

Users are asked if they want to use HomePods as default TV speakers
What comes next?
At this time, Dolby Atmos cannot be enabled when two HomePods are paired with Apple TV 4K. However, it is not hard to imagine that Atmos, or some form of object-based audio, would be supported for games in the future.
We were not able to set HomePod as the default speaker for Apple TV HD. We are not sure if that is intended behavior or a bug.
Apple is rumored to be pouring "big money into" its game service, Apple Arcade, and to be planning new Apple TV boxes with "A14X-like" and A12X/A12 SoCs.
tvOS 14.2 is expected to be released publicly later this year.
- thanks for the tip, Henry!