When I get a new holster , I've never owned a lined one, I melt a little beeswax and rub it into the insides , once I get a good layer rubbed in , I use the hair dryer on the insides to melt the beeswax so it will soak in the surface a little , any excess can be removed with a paper towel and heat.
The beeswax does not soften the leather but does put a waxed surface between the leather and the guns finish.
I find the wax better than neatsfoot oil or any grease that will soften the leather.
Gary