Jensen was already training continuously with the first-team squad at age 16 and on 20 November 2020, he signed a three-year contract with the club.[3] 17-year old Jensen got his official debut for SønderjyskE against Fremad Amager in a Danish Cup game.[4] This was his only appearance in the 2020-21 season.
In the 2021-22 season, he got his debut in the Danish Superliga age 17 in a match against Randers FC on 8 August 2021.[5]
St. Louis City
On 11 July 2022 it was confirmed, that Jensen had been sold to American MLS side St. Louis City, who would begin play in the 2023 season, with the player signing a deal until the end of 2026, with an option for one further year.[6]
Viborg FF
On 30 August 2023, Danish Superliga club Viborg FF confirmed that they had loaned Isaksen from St. Louis City for the 2023–24 season, with an option to buy at the end of the loan.[7] The loan moved proved to be successful as he scored seven goals from 27 appearances for the club, playing a key role in their late-season success. His first goal for the club came on 1 October, as Viborg defeated AGF 2–1.[8]
On 25 May 2024, it was confirmed by Viborg that they had decided to exercise their option to purchase Jensen. He signed a three-year contract with the club.[9][10]