Iosivas played on Princeton's junior varsity team as a freshman. As a sophomore, he caught 18 passes for 263 yards and four touchdowns.[4] Iosivas's initial junior season in 2020 was canceled due to the COVID-19 pandemic and he took a gap year.[5] In 2021, he caught 41 passes for 703 yards and five touchdowns and was named second-team All-Ivy League.[6][7] Iosivas entered his senior season as the 15th-most athletic player in college football on sportswriter Bruce Feldman's annual "Freaks List".[8] He was named first team All-Ivy League after leading the conference with 66 receptions, 943 receiving yards, and seven touchdown catches.[9]
Iosivas was also a heptathlete on Princeton's track and field team.[10] He set the school record with 5,715 points in 2022 and was named an All-American.[11][12]
He made his first career reception, a 9-yard contested sideline catch, in the Bengals' Week 5 game against the Arizona Cardinals.[16] In Week 6 against the Seattle Seahawks, Iosivas scored his first career touchdown on a 3-yard pass from quarterback Joe Burrow in a game the Bengals won 17–13.[17] Iosivas grabbed his second career touchdown on an 2-yard pass against the San Francisco 49ers in what ended up being his only target of the game.[18] Iosivas missed the Bengals' Week 11 contest against the Baltimore Ravens due to a knee injury.[19]
In Week 18 against the Cleveland Browns, Iosivas played his first career game as a starter, due to Tee Higgins re-aggravating a hamstring injury. Iosivas had a solid game, with five receptions on seven targets for 36 yards and two touchdowns.[20] He finished his rookie season with 15 receptions, 116 yards, and four touchdowns.