On February 3, 2021, Alexander recorded 16 points, six assists, four rebounds and three steals in a 70–59 upset win over third-ranked
Villanova. In his next game, on February 6, he posted a freshman season-high 21 points and six assists in a 92–81 victory over
Providence. Three days later, he earned USBWA National Freshman of the Week honors. At the end of the regular season, Alexander was named
Big East Co-Defensive Player of the Year and
Big East Freshman of the Year. He became the fourth player to win both awards, joining
Allen Iverson,
Alonzo Mourning and
Patrick Ewing. He was a unanimous Big East All-Freshman Team selection. As a freshman, Alexander averaged 10.9 points, 4.3 assists, 3.4 rebounds and 2.6 steals per game. He led the Big East and all freshmen nationally in steals per game. Alexander averaged 13.8 points, 5.5 assists, 4.4 rebounds, and 2.3 steals per game as a sophomore. In his junior season at St. John's, Alexander averaged 10.2 points, 4.2 assists, 3.9 rebounds, and 2 steals per game. After the season, he decided to stay in the Big East and transfer to Butler. On November 30, 2023, Alexander posted the first triple-double by a Bulldog player since
Roosevelt Jones in 2016. He had 10 points, 10 rebounds, and 11 assists in a 103-95 overtime win over
Texas Tech in the
Big East-Big 12 Battle. On December 9, 2023, Alexander recorded a season-high 21 points in a 97-90 double overtime win over
California. On January 16, 2024, Alexander tied a season-high with 21 points in an 85-71 loss at
Xavier. In his senior season at Butler, Alexander averaged 11.3 points, 4.9 assists, 4.6 rebounds, and 2.2 steals per game. After Alexander's senior season at Butler, he decided to transfer to Dayton for his final season of collegiate eligibility. He averaged 5.8 points, 2.2 rebounds, and 2.2 assists per game. ==Professional career==