What Is Up with Apple TV 4K's Surround Output?

[VanHiscers]

I have an Apple TV 4K (1st Gen), and my original set up was to have Apple TV connected to my TV, and my TV is connected to my soundbar system via e-Arc. My TV was set to pass through all compressed multichannel signals, while the Apple TV audio setting's "change format" was set to off to preserve Dolby Atmos capability.

Before the TVOS 18 update, the Apple TV was smart enough to recognize my TV's passthrough ability, and re-encode multichannel signals into Dolby Digital, while sending out Dolby Atmos signal when available.

After the TVOS 18 update, however, My Apple TV 4K can no longer detect my TV's passthrough ability, and only send multichannel PCM signals to the TV, while the TV will only interpret it as stereo PCM and send it to the soundbar.

Some say the beta updates fixed it, but that didn't happen. The only work-around for me at the moment was to connect Apple TV 4K to the soundbar directly, as the soundbar can handle multichannel PCM signals correctly. Nevertheless, Amazon Prime Video app's Dolby Atmos is still not working...

Does anyone know if this is only affecting the 1st Apple TV 4K, or all models? Thanks!