I don’t think games are outright fixed or anything but I do think the NFL occasionally puts their finger on the scale with the help of the officials.
Even with replay, the officials make some of the most baffling calls at times and it always seems to help certain teams and go against other “lesser” teams.
I can’t tell you how many times over the years I’ve watched the Pittsburgh Steelers go into the final 2 minutes trailing by a touchdown or less and suddenly things that have been going on the entire game are now defensive holding, pass interference, etc.
It’s definitely there.