Hello William3241,
Welcome to Microsoft Community.
Let me help you solve the problem of not supporting HDR.
Your two monitors originally supported HDR, but the problem occurred after updating the system, right?
If the problem occurred after the update, it may be caused by the incompatibility of the monitor driver or graphics card driver with the latest system.
You can consult the manufacturer of the device, whether the current monitor and graphics card drivers support HDR function, if not, please replace the supported drivers.
If the driver supports the HDR function, the system still prompts unsupported, then I recommend that you uninstall the latest update to see if it can be resolved.
Open Settings > click Windows Update > Update history> Uninstall Updates > click the update you want to uninstall > click the "Uninstall" button above.
In addition, the following link is to a support document I found for HDR setup in Windows that you can learn about.
HDR settings in Windows
If there is anything not clear, please do not hesitate to let me know.
Best Regards,
Lenka-MSFT| Microsoft Community Support Specialist