I've been seeing reports around the interwebs that "the new Apple TV 4K is only giving me HD (2K) video for 4K shows". The proof being cited is often via the "swipe-down" menu while in an app like Netflix or Showtime Anytime that supports the Info section. In the Info section it usually contains the program's name, and an icon beside it that should say HD or 4K. Note that not all apps support that section, my HBO Max and Disney+ app do not have the Info section when you use the swipe-down menu, just Audio and Subtitles.
So I decided to test this out, and I took some pics for proof. I downloaded XCode on my Mac and paired it to the ATV4K v2. I then enabled the Developer HUD on the ATV (you can easily google instructions on how to do this). The HUD gives you the actual stream data. What you're looking for is the "natural-size" value, not the "resolution" value, because if you have your ATV set to upscale everything to 4K the resolution value will always be 3840x2160. The "natural-size" will tell you what the incoming resolution is from the streaming service.
Here is the problem in a nutshell. Below is the swipe down Info section for Lucifer S5E1 on Netflix, which should be a 4K episode.

Note how it says "HD" right beside 51 min, as opposed to 4K. This is what is making people think they're only being delivered HD content.
However if you look at the HUD data (I just exited out of the swipe-down menu), you see this:

Note natural-size value of 3840x2160. That's 4K. And if you look at the avg and peak bit rate, it's 17Mbps and 25Mbps which is definitely 4K range (Netflix HD bit rate is mostly in the single digits, like 3-7Mbps).
And just to show that the natural-size isn't just lying to us, here's S1E1 of Lucifer, which was not a 4K episode:

Note how natural-size is 1920x1080 and the avg bit rate is 3.88Mbps
Here's the HUD for Away, on Netflix, to again show it not only shows 4K, but also supports Dolby Vision (says it up top "video-range: DolbyVision 5")

And here's Wonder Woman 84 on HBO Max, to again prove it's showing 4K Dolby Vision

Hopefully Apple will fix the labeling issue. I think they own the swipe-down menu since it cuts across all apps, it is part of tvOS, so I think the fault is theirs to find and fix. Because they're starting to take criticism from those believing they're only seeing an HD signal when in fact they're getting the 4K (assuming their bandwidth is sufficient and they're subscribing to the appropriate tier of service) but the swipe-down is just mislabeling it as HD.
So I decided to test this out, and I took some pics for proof. I downloaded XCode on my Mac and paired it to the ATV4K v2. I then enabled the Developer HUD on the ATV (you can easily google instructions on how to do this). The HUD gives you the actual stream data. What you're looking for is the "natural-size" value, not the "resolution" value, because if you have your ATV set to upscale everything to 4K the resolution value will always be 3840x2160. The "natural-size" will tell you what the incoming resolution is from the streaming service.
Here is the problem in a nutshell. Below is the swipe down Info section for Lucifer S5E1 on Netflix, which should be a 4K episode.

Note how it says "HD" right beside 51 min, as opposed to 4K. This is what is making people think they're only being delivered HD content.
However if you look at the HUD data (I just exited out of the swipe-down menu), you see this:

Note natural-size value of 3840x2160. That's 4K. And if you look at the avg and peak bit rate, it's 17Mbps and 25Mbps which is definitely 4K range (Netflix HD bit rate is mostly in the single digits, like 3-7Mbps).
And just to show that the natural-size isn't just lying to us, here's S1E1 of Lucifer, which was not a 4K episode:

Note how natural-size is 1920x1080 and the avg bit rate is 3.88Mbps
Here's the HUD for Away, on Netflix, to again show it not only shows 4K, but also supports Dolby Vision (says it up top "video-range: DolbyVision 5")

And here's Wonder Woman 84 on HBO Max, to again prove it's showing 4K Dolby Vision

Hopefully Apple will fix the labeling issue. I think they own the swipe-down menu since it cuts across all apps, it is part of tvOS, so I think the fault is theirs to find and fix. Because they're starting to take criticism from those believing they're only seeing an HD signal when in fact they're getting the 4K (assuming their bandwidth is sufficient and they're subscribing to the appropriate tier of service) but the swipe-down is just mislabeling it as HD.