When looking at the Stanford schedule, it appears that BYU is taking the opportunity to fill the Thanksgiving weekend Stanford/USC game that they need to fill late in the conference schedule season when many non-independent teams aren't available.
Thanksgiving Weekend Football Game
2020 - Stanford vs BYU, USC vs Notre Dame
2021 - Stanford vs Notre Dame, USC vs BYU
2022 - Stanford vs BYU, USC vs Notre Dame
2023 - Stanford vs Notre Dame, USC vs BYU
2024 - USC vs Notre Dame **Stanford @ Notre Dame earlier in October
2025 - **Stanford @ BYU in September
2026 - Stanford vs BYU*, USC vs Notre Dame
2027 - **BYU already has 3 games in September
2028 - Stanford vs BYU*
2029 - **Stanford @ BYU in September
2031 - *Stanford @ BYU in August
2035 - *Stanford @ BYU in September
* Newly added to the series
** Description of other notes
The PAC12/ND Thanksgiving game is not there in 2025 or 2027 but BYU fills in the 2026 slot with the new agreement and fills the 2028 spot for Stanford, though Notre Dame doesn't have anything in that spot on their schedule yet. Needing return games, the 2031 and 2035 games are probably fitting Stanford needs since they can only schedule 3 OOC games per season. If I'm BYU, I'm taking any of those Thanksgiving weekend games with either USC or Stanford as they are well publicized against a good opponent at a spot that is tough to fill otherwise.