Johnson grew up in
Dallas, Texas and attended
Lake Highlands High School. He averaged 23.8 points, 5.6 rebounds and 2.3 assists per game as a sophomore. During his junior year, Johnson and Lake Highlands took part in the City of Palms Tournament, where he averaged 23 points per game. At the end of the season, he led Wildcats to their first state championship since 1968 and scored 29 points in the team's 55–44 win in the state championship game against
Beaumont United High School. Johnson finished the season averaging 21.8 points, 6.4 rebounds and 2.7 assists per game and was named
Texas Mr. Basketball. After the end of the school year, he transferred to
Link Academy in
Branson, Missouri. Johnson produced 15.5 points, 3.6 assists and 3.3 rebounds per contest while shooting nearly 40% from 3-point range and 90.5% from the free throw line during his senior year. Johnson led the Lions to a 26–7 record. Johnson was selected to play in the
2024 McDonald's All-American Boys Game during his senior year.
Recruiting Johnson was a consensus five-star
recruit and one of the top players in the 2024 class, according to major recruiting services. He was ranked the top overall recruit by
247Sports,
ESPN,
Rivals, and
On3 throughout his junior year until he was surpassed by
Dylan Harper during the summer of 2023. On November 15, 2023, Johnson committed to playing college basketball for
Texas after considering an offer from
Baylor. ==College career==