Thanks!  I think I found the way to retain settings.  Using the "Win+ALT+B" shortcut in Windows 11 to flip from HDR to SDR, the monitor honors my default settings and properly swaps between my vibrated Custom SDR preset and True Black 400 HDR.  Looks like I am all set!
Windows 11 user here.  Just got this Dell Alienware monitor and it is incredible. I calibrated it with an i1 Display Pro in the custom SDR picture setting and let DisplayCal manage the profile association (have an Nvidia 3070 GPU).  To support the high refresh rate of the monitor, I must create a custom resolution in the Nvidia Control Panel and bump the refresh to 144Hz and color bit depth to 10bit.  The question I have is that I would like to switch between SDR and HDR modes but every time I swap to HDR then back to SDR, all my settings get cleared.  I must recreate the custom resolution, set desktop scaling to 125%, reenable the DisplayCAL ICC profile, etc. as if it was the first time I setup the monitor in Windows. This could quite possibly be a Microsoft or Nvidia question, but does anyone have a suggestion to allow swapping between picture modes (SDR to HDR and back) without wiping the SDR color and resolution settings in Windows?  Windows does have a shortcut to do this. Thanks!
AW3423DWF and switching between SDR and HDR modes