Infinity Transmission issues

2009 FX 35 has 2 driving options for transmission…traditional D for Drive and DS for Sport/shifting gears manually which makes the car fun to drive.
Recently the car decided it no longer wants to allow driving in the DS Sport mode…when shift into DS it simply stays in Drive.
No issues with Drive option functioning but it isn’t fun to drive that way.
I’m told that the transfer case might be the problem…can it be fixed?
…or is there some other thing more likely?

EVERYthing can be fixed. It just costs money. And I doubt the transfer case has anything to do with it, especially if you have a rear wheel drive version of the car.

It could be a problem with the shifter itself or the transmission or some electronics between the two. I’d start with the shifter myself since it still drives and shifts OK.