As a freshman in 2016–17, Johnson averaged 15.2 points, 6.2 rebounds, 2.1 assists, 1.2 steals, and 1.1 blocks to help his team to a 20–4 record.

As a sophomore in 2017–18, Johnson averaged 18.4 points, 9.6 rebounds, 4.0 assists, 1.9 steals, and 1.5 blocks to help his team to a 25–2 record.

After his sophomore year he transferred to Nicolet High School in Glendale, Wisconsin.

[2] On January 5, 2020, he left IMG Academy, before returning to Nicolet, though not necessarily to play basketball.

[5] On July 4, 2019, Johnson committed to play college basketball at Duke University over offers from Arizona, Kentucky, and Wisconsin.

[6][7] Sources: The 2020–21 Duke Blue Devils team entered the season in the top 10, and Johnson was its most highly rated player.

[10] On February 15, 2021, Johnson announced that he would forgo the remainder of Duke's season to prepare for the 2021 NBA draft.

Leaving in the midst of a college season raised many questions, with Johnson claiming that the decision was in the best interest of his family and himself.