PFF currently ranks Book #29 nationally among QBs, but notes that he's trending positively. From the linked material:
"There were some massive concerns with Notre Dame's quarterback situation leading up to the program's game against Clemson, as Ian Book wasn’t performing at a level that could get the Irish to CFP-contention status. He put together just a 60.3 passing grade in his first six starts against middling defenses but balled out against the Tigers in Week 10 — his 90.7 passing grade that game was the highest of his career against a Power 5 school. He continued that caliber of play this week against Boston College, as Book came away with his second-best passing grade of the season and led the Irish to the third-most efficient passing offense in the Power 5. His reluctance to throw the ball downfield has disappeared, and he has gotten his accuracy back to the level it was back in 2019. Book’s negatively graded throw rate ranks first among the 39 qualifying Power 5 quarterbacks over the last two weeks."
I don't know if Book has a real NFL career ahead of him or not, but I agree with ndunabomber that he "has nothing to gain" by returning to ND next season.
Link: https://www.pff.com/news/college-football-ranking-all-127-fbs-quarterback-situations-ahead-of-cfb-week-12