Answering my own question. Maryland starting in 2022.
Weird.
B1G 10 Cross-Division Football Rivals
That was the case previously, but I thought that might have been subject to change post the Covid year. But based on this site, which has usually been reliable in the past, it seems like as of now those protected matchups will take place as previously scheduled starting in 2022 (the first link is for 2021 schedule, you can toggle the year forward.
View the 2021 Northwestern Football Schedule at FBSchedules.com. The Wildcats football schedule includes opponents, date, time, and TV.
fbschedules.com
Crossovers
2021: MSU, @Mich, Rutgers
2022: @Indiana, @Maryland, OSU
2023: @Rutgers, PSU, Maryland
2024: @MSU, Mich, @Maryland
2025-2027 are just the inverse of 2022-2024 (home matchup turns into road game and vice versa)
Overall it's not a bad draw, if it doesn't get changed. Btw we play Duke every year until 2024. Other than that not many interesting OOC matchups scheduled as of yet. I do like the home-and-home with Colorado in 2026-2027. Also we open with a B1G crossover game each of the next 3 years - MSU in 2021, Indiana in 2022, Rutgers in 2023.