Quote The title covers it. It's just a simple question. Unchecking the "Enable Hardware Acceleration" box in the settings menu does nothing, and I can't seem to find an option for it in my OS settings.

If you unchecked the hardware acceleration option in powerdvd settings, gpu decoding will not be applied during Blu-ray playback.
Enabling TrueTheater video effect for playback will disable the hardware acceleration automatically, too.

I have no idea that your "unchecking the ... box does nothing" means or what you want exactly.
Per my understanding, gpu decoding generally delivers better playback performance than cpu decoding (disable hardware accleration).

Having unchecked the box in question from the "Video, Audio, Subtitles" tab, the "Information" tab still displays that DXVA is in use when checked during Blu-ray playback, whereas the same tab indicates that DXVA is not in use during DVD playback. I'm using Windows 10 (64-bit), if it makes a difference.