On average, college grades are lower than high school grades. Probably most high school students who go on to college had HS GPA of 3.0 or higher. But college students’ GPAs range from 2.0 to 4.0 (with some lower and flunking out for academic reasons).
At the super-selective end of colleges, most incoming frosh have 3.8-4.0 HS GPA. But even those with the highest average college GPAs like Brown or Harvard have average college GPAs in the 3.6-3.7 range.
Of course, individual students may have college GPAs better or worse than their high school GPAs.