I'm not clear on how cfbstats computes qb rating, but Mac Jones has the highest recorded on their site.
The best-ever pass rating has increased every year for the past 5 years. Literally. It's stupid.
The highest-rated season pre-2000 was Shaun King's 1998 season at Tulane. The highest P5 going back was Wuerffel's non-Heisman 1995 season.
Check out the "best ever" single-season QB rating lineage:
1964 - Jerry Rhome, Tulsa (172.6)
26 years later
1980 - Jim McMahon, BYU (176.9)
15 years later
1995 - Danny Wuerffel, Florida (178.4)
3 years later
1998 - Shaun King, Tulane (178.8)
6 years later
2004 - Stefan Lefors, Louisville (181.7)
2 years later
2006 - Colt Brennan, Hawai'i (186.0)
5 years later
2011 - Russell Wilson, Wisconsin (191.8) - Robert Griffin III broke it, too
5 years later
2016 - Baker Mayfield, Oklahoma (196.4)
2017 - Baker Mayfield, Oklahoma (198.9)
2018 - Tua Tagovailoa, Alabama (199.4) - Kyler Murray broke it, too
2019 - Joe Burrow, LSU (202.0)
2020 - Mac Jones, Alabama (202.3) - with 1-2 games to go