Mangum has been great against the Little Sisters of the Poor, but he's been average or bad against P5 defenses.

Your OL is good inside, but Lotulelei and Mokofisi will be better, and your line is average on the outside, where Anae and Fitts will get pressure on Mangum (who is bad against P5 defenses, and worse under pressure).

Utah's OL will be fine at Tackle (Barton and Uhatafe are both NFL OL), and the interior of your DL isn't very good (or hasn't shown much) to take advantage of the less-experienced guards. Your Linebackers will be good, obviously, especially against the run, but they're not super athletic in coverage, which leads to Utah's TEs (Handley is a monster) and RBs (both Shyne and Moss are better than any BYU RB) being open in the flat.

BYU won't have any chance to run the ball against Utah's DL/LB, so you'll have to rely on Mangum, who (as outlined above) isn't really very good. Plus he has nobody to throw to except Trinnaman and MLP. MLP will be shut down by Luafatasaga and any of Utah's corners can cover Trinnaman. On the other side, BYU's secondary is average at best, and while they're experienced, Utah has 4 WR (Carrington, Singleton, Simpkins, Wilson) better than any WR on BYU's roster, not to mention the 4* incoming WRs (Thompson and Hampton).

I expect a higher-scoring game than normal, because both teams are going to throw the ball more than average. Let's say 42-17 for Utah.