An undefeated record against the 2020 schedule wouldn't have been good enough to prove BYU was a top 4 team.
Unless Arizona State, Baylor, Virginia, and USC have really nice seasons, an undefeated record against the 2021 schedule won't be enough to prove BYU is a top 4 team.
The bar is the same, 2021 is closer to meeting it but most likely will still fall short. If you swapped Arizona with Oregon or Wazzu with Penn State, then that would probably be enough.