[1] On 5 May 2024, 17-year-old Højer was on the bench for Copenhagen's first team for the first time in a Danish Superliga match against Silkeborg IF.
[4] He made his Copenhagen debut on 25 July 2024, substituting for Magnus Mattsson in a UEFA Conference League qualifier against FC Bruno Magpies.
[5][6] In the return match on 1 August 2024, he made his debut at Parken Stadium, again substituting for Mattsson and scoring his first goal for the club.
[7][8] On 11 August 2024, Højer made his Danish Superliga debut in a match against Sønderjyske.
[9] On February 2, 2025, Copenhagen announced that Højer had been injured and was facing surgery.