Q: Will my Mac 10S 10.8.5 open up the raw files from the new Nikon D500 with regular PS6 andACR?

Hi mR.december23,
 

Thank you for visiting Apple Support Communities.
 

I see you're wondering if OS X 10.8 (Mountain Lion) will support RAW files from a Nikon D500. It looks like RAW file support for this camera (Nikon RAW L format only) was added in a recent update, and this update requires OS X El Capitan.
 

You can find this information here:
 

Digital camera RAW formats supported by OS X El Capitan
 

Digital Camera RAW Compatibility Update 6.19
 

All the best.