From what I understand, Netflix only has HDR on 4K 10 bit programs at 60p and that requires the latest 18Gps HDMI chipset. Mine ( Sony) is limited to 10 bit at 24p so I can't get Netflix HDR anyway. Amazon HDR is all at 24p and the content looks good. I don't understand why Netflix did that as there aren't that many systems available with the 18Gbs HDMI. JVC Projectors has it but it is not true 4K but an upscaled 2K eshift to 4K as I understand.
Netflix on the Roku is like 420 color space though, so the bandwidth should not be an issue. I have easily gotten Netflix HDR on blu-ray players, the Roku, and the Shield.
Most of the JVC owners on AVS are not using HDR anyways, it takes a FP with outstanding blacks and raises them. They are using SDR 2020 with a Panasonic 900.