Holmberg skated in 45 games for Växjö in 2020-21 and recorded 23 points (nine goals, 14 assists) before collecting 14 points (seven goals, seven assists) in 17 playoff games for the club, winning the SHL Championship and earning recognition as the SHL Playoffs MVP. He was also named the SHL's Swedish Forward of the Year. In 146 career SHL games, all with Växjö, the Västerås native has recorded 50 points (19 goals, 31 assists).
Internationally, Holmberg represented Sweden at the 2021 IIHF World Championships and skated in a pair of games at the tournament. He previously represented Sweden at the 2019 World Junior Championship and appeared in five games.
Holmberg was selected by the Maple Leafs in the sixth round (156th overall) of the 2018 NHL Draft.
