There are several considerations for an HDR monitor:

• Peak brightness (in nits, aka cd/m^2).
  • This is the single most important criteria for HDR display. If the monitor doesn’t get bright enough, it will offer at best a mediocre HDR experience.
  • The absolute minimum for HDR support is 400 nits. A monitor at this level will offer about 1 stop of HDR when viewed at half brightness. That can offer a good experience when viewed in a dim room, but you wouldn’t get much benefit if the screen is near a window or outdoors.
  • 600 nits is a noticeable step up over 400, but still just a decent HDR experience.
  • 1000+ nits is where HDR gets truly exciting. Anything in this range will look excellent for HDR in a range of viewing conditions.
• Deep blacks
  • Most monitors use a single backlight to illuminate multiple pixels. Some of this light will bleed through with a black pixel, meaning that it is not truly black.
  • HDR quality is ultimately about achieving a greater dynamic range, and having a washed out black (not truly black) reduces dynamic range.
  • Some monitors (such OLED or future “micro” LED displays) can achieve true black. You may see such monitors marketed as having “infinite” contrast (since you’re dividing the brightess white pixel by a black pixel that is considered to be 0 nits).
  • The benefit of deeper blacks is much more apparent in a dark room. 
  • While a darker black pixel is important, the peak brightness is still more important as your monitor needs to be bright enough to compete with ambient light.
• How does the monitor look with a reference image?
  • There are so many considerations that there is no substitute for seeing the monitor yourself.
  • If you are comparing monitors in a store, use Google Chrome to view my tests and example HDR images. Be especially sure to use test #8 to check the HDR headroom. This shows the real HDR benefit at the current monitor brightness (and SDR content brightness for Windows).
  • Check system settings to ensure HDR is enabled in Windows or the display settings for an HDMI monitor on MacOS.
  • Check that the SDR content brightness is 0-50 (if this slider is set too high on a 400 nits monitor, you won’t have any HDR headroom at all).
  • Check that the monitor settings (brightness, etc) are reasonable.
• Non-HDR considerations:
  • Look for a monitor which covers most or all of either the P3 or Adobe RGB gamut. Most HDR images will still look with a limited sRGB gamut, but don’t limit yourself to colors from the ’90s.
  • You can experience HDR at any resolution and 4k resolution isn’t very important for photography with even 32″ monitors. Unless you’re editing 4k video, this is a place to consider saving some money.
  • If you are going to evaluate images for print with your HDR monitor, all the standard considerations apply in terms of even illumination, etc. That said, I’ve made a lot of large prints using a budget monitor with proper calibration and profiling. Learn more about considerations for printing with HDR workflows here.
  • High refresh rates are helpful for gaming, but not important for photography – and you may need use less than the maximum refresh rate in some setups to use HDR.
• Price
  • HDR monitors are definitely a bit of an investment. Costs should start to come down as volumes increase in the coming years. The general range in late 2022 is about $500 – $3000 for most consumer options (but you can find $300 options and spend $35k on an HDR reference monitor).
  • If you’re on a tight budget, you might wait a while or purchase a 400-600 nits monitor if you will be able to use it at half brightness.
  • If you have a larger budget, get a 1000+ nits monitor for an outstanding display. The benefits of HDR increase substantially with these brighter monitors.
• GPU / video card / codec
  • Microsoft customer support indicated that there is no specific GPU or video card requirement to enable HDR in Windows 10 or 11 so long as you have an HDR monitor.
  • I’m not 100% confident that there aren’t exceptions to that, but I am not aware of any at this time.
  • Apple explicitly lists their compatible HDR hardware here.