On a points-per-game level against Big 12 opponents, BYU has the #1 offense and #5 defense in conference, while Utah has the #15 offense and #2 defense.
BYU has played the the #3, #6, #8, #13, and #14 Big 12 offenses, and #8, #12, #14, #15, and #16 Big 12 defenses. Based on this, BYU's offense has played relatively weak defenses to this point in the season, while their defense has played a spread of offensive quality.
Utah has played the #3, #9, #11, #13, #14, and #16 Big 12 offenses, and #6, #7, #10, #14, #15, and #16 Big 12 defenses. Based on this, UU's offense is just as bad if not worse than we imagined, but the defense has also played a spread of offensive quality (and that's while missing 4-5 key players from the 2-deep of their front 7).
Common opponents are Baylor and Arizona. Utah beat Baylor at home 23-12, though a healthy Cam Rising started that game, and Baylor's QB Robertson (who has been a revelation this season starting with the BYU game), did not play against Utah. Utah lost to Arizona at home 10-23, while BYU beat Arizona at home 41-19.
BYU has been winning Big 12 games by an average score of 38-23. They score approximately 4 points more than opponents' defensive averages, and hold opponents to about 5 points lower than their offensive averages.
Utah's Big 12 games have an average score of 16-19 (and if you take out the Baylor game, it drops to 14-20). They score 16 points (!) fewer than opponent's defensive averages, and hold opponents to 7 points lower than their offensive averages.
Taken together, BYU likely scores somewhere in the range of 20-27 points this Saturday against the best Big 12 defense they will play this regular season, though BYU also boasts the best Big 12 offense the Utes will have faced all season. On the other side, it's hard to see how Utah scores more than 13 points this Saturday, as BYU has the best Big 12 defense Utah will be facing all regular season.
Make no mistake, Utah's defense is legit, especially with getting a bunch of their front 7 players back from injuries. BYU hasn't faced a defense this good since SMU, so their streak of scoring 30+ points likely ends this Saturday, but as long as they break 20 points, it should be enough for the win as long as they take care of the football.
The most likely score I think for BYU will be something along the lines of 23-13. Best case scenario would be UU's offense imploding with TOs and 3-n-outs, with a final score of something like 31-9. Only realistic chance I think Utah has of winning is being at least +2 in the turnover margin, including a D/ST touchdown, and winning something like a 16-13 type of game. Regardless, this game is likely tight in the 4th quarter, as even during their 4 game losing streak, Utah held leads in two of the 4th quarters, and 3/4 losses were within 1 score.