Baker, Saginaw Valley State, Northern Michigan, Pacific, Wesleyan, Eastern Illinois, Mount Union, Dayton, Penn, 2 from William & Mary & 2 from Miami (OH).
That's 13, or 41% of NFL head coaches in the 2021-22 season who did not play Power 5 college football.
The SEC, who supplies the NFL with the most on the field talent by a wide margin, has exactly one head coach (Dan Campbell, Texas A&M).
Sean McVay was the Georgia high school football player of the year in the same class with Calvin Johnson. While Calvin Johnson was beginning the second season of his pro career, McVay had finished college and was beginning his coaching career with the Tampa Bay Buccaneers. In 2016 when Johnson retired, McVay (who had been coaching pro football for eight years now) had worked his way up to offensive coordinator of the then Washington Redskins.
That's why former players have trouble getting head coaching jobs. While they were playing, the people they are interviewing against were coaching.