The last spot would come down to:
5th SEC team
2nd ACC team
2nd Big 12 team
4th Big 10 team
There are just too many scenarios at this point. BYU's best chance is to not lose more than 2 games (including the Big 12 championship game) and hope that SMU either wins the ACC or at least plays in the championship game (not impossible). BYU though has to win the close games. They did it in 2021 versus the Pac 12 so they are capable.