Mac Studio M4 Max and BenQ PD3226G Display: HDR and Refresh Rate Limitations

So, after trialling the BenQ PD3225U 4K monitor with my new Mac Studio M4 Max, I am comparing it with the PD3226G 4K. I have 2 immediate questions:

1) the monitor is 144Hz, so why can I only set it to 100Hz in Settings>Display?

2) HDR is not available unless I lower the frequency from 100Hz to 60Hz. Is this correct?

Thanks in advance.

[Re-Titled by Moderator]