Millner was raised in Little Rock, Arkansas, and played basketball, baseball, and football while growing up.[1] His mother convinced him to focus on one sport so he committed himself to basketball.[1] At a ninth grade Amateur Athletic Union (AAU) tournament in Indianapolis, Millner fractured his tibia in a fall and was confined to a wheelchair for several months.[1] He was unable to attend his high school in Little Rock as it did not have elevators so he was offered by his cousin, Duane Washington Jr., to move in with his family in Grand Rapids, Michigan, and attend Grand Rapids Christian High School which had elevators.[1] Millner recovered from his injury during his sophomore season and played on the junior varsity team.[1] As a junior, he led the team to a 26–1 record and a second-place finish in the state tournament.[2] Millner averaged 20.1 points, 9.4 rebounds and 3.6 assists as a senior.[2] He also joined the football team as a wide receiver during his senior year and earned scholarship offers in both sports.[1]
Millner started all but one game as a freshman with the Vikings.[4] The team lost 21 games and Millner opted to transfer after the athletic director made changes to the personnel.[4] Millner spent the following season playing at Northwest Florida State College.[4] He was recruited by Toledo Rockets head coach, Tod Kowalczyk, while playing at Northwest Florida State and transferred to play for the Rockets during the 2020–21 season.[1]
Miller played three seasons for the Rockets and averaged 14.8 points as he helped the team to a 74–25 record.[5] The Rockets won three consecutive league titles in the Mid-American Conference (MAC) during his tenure.[5] Miller was named to the All-MAC second-team in 2023 and third-team in 2022.[5]
On April 30, 2022, Millner's father, Setric Sr.,[10] was fatally wounded in a Little Rock shooting.[11] Murder charges against the suspect were dropped due to a lack of witnesses.[12]
