Hello,
I'm not sure if there is an issue with Mt Denali. I was flying toward it from the south and the top was mostly black. The north side wasn't as bad. I'm running FS4 on a Mac mini M2 with 8GB ram. I've attached some screenshots. The first two are from the south and southwest. The last one from the north. I don't remember the in-game time of day but I'm guessing mid afternoon. I noticed it was black on the flight plan map too. I flew west of the flight plan (so I wouldn't hit the mountain )
Thanks,
MG.