Moonlight works really well on the ATV4K too. I stream 4K@60FPS with HDR and surround sound from my PC using the Apollo fork of Sunshine (creates a virtual display since I normally game at 1440p on my attached monitor).

I'm quite "technical" so to speak yet trying to properly set up HDR in Sunshine was rough.

I think this is one of the things that the Apollo fork[1] makes way easier. I'm not sure that I had to do anything Apollo config wise* . I just went through the Windows HDR calibration tool the first time to tune it for my TV and it was good after.

*I do have a once-per-run Moonlight glitch that may even be because I'm on an older version. The first connection just doesn't pick up on the HDR immediately. I just have to reconnect once and it's good after that.

[1]: https://github.com/ClassicOldSong/Apollo ("Built-in Virtual Display with HDR support that matches the resolution/framerate config of your client automatically")

They just updated the moonlight client which I’m sure you’re on should be more reliable and I highly recommend https://github.com/Nonary/Vibepollo fork of Apollo

I found the input latency to be much worse than the PC connected to the same TV, for whatever reason.

I thought I surely was imagining it, so I revisited it 6 months or a year later, and, yes, the input latency from the controller is substantially worse on the Apple TV.

Does your TV (not the Apple TV) have a "game" mode picture mode in its settings?

I had unacceptable input lag when streaming to my Apple TV 4k, but switching the TV it into "game" mode fixes it entirely. I just need to swap it over to game mode when I hop into Steam Link or Moonlight.