Probably really FAKE HDR like the Fake HDR done for the Star Wars movies on Disney+.
Wouldn't surprise me since Netflix also has "Fake Atmos" since I usually can't hear much from the ceiling speakers.
So probably usually FAKE 4K (just 2K upscaled to 4K), FAKE HDR, and FAKE Atmos.
Even though it will show up as "4K, HDR, Atmos".
BTW, I've seen some regular 2K SDR movies and TV shows with colors so vibrant and beautiful that look like "HDR".