I have the ks8000 and pc mode looked different until I realized the settings didn’t match my other inputs. Once I put the same settings in my tv as I did the other inputs they looked the same on Pc mode. Before I realized that I also was switching to “game console” but like the OP said it would auto change some times which was annoying.
If the picture settings of your tv is the same between pc and your other inputs but the picture is still different(especially if the pc mode is a dark picture) turn off the ECO setting on your Samsung. Mine would auto dim in pc mode and even sometimes constantly cycling bright dark bright dark until I read on the internet to turn that eco setting off.
I can now leave my tv on pc mode and get the same picture.