On 7 June 2019, Ivanušec was selected in Nenad Gračan's 23-man squad for the UEFA Under-21 Euro 2019. He made two appearances at the tournament, in the 1–0 defeat to France and the 3–3 draw with England, as Croatia finished last in their group. In the latter match, he provided Josip Brekalo with an assist for Croatia's third goal. On 9 March 2021, he was once again selected for the UEFA Under-21 Euro 2021, being named in Igor Bišćan's 23-man squad for the group stage of the tournament. He stuck out as one of the best players in the team, as Croatia progressed to the quarter-finals. In the final group game, the 2–1 loss to England on 31 March, Ivanušec made his 27th appearance for the team, becoming its most capped player in history. On 17 May, he was named in Bišćan's 23-man squad for the knockout stage of the tournament, as well as Zlatko Dalić's 26-man squad for UEFA Euro 2020. On 7 June, he was listed in the UEFA Under-21 Euro 2021 Squad of the Tournament.