On 7 December 2019, Mangas made his professional debut in Primeira Liga for Aves, playing the full 90 minutes of a 1–0 home win against S.C. Braga; he was watched by Atlético Madrid forward and Portugal international João Félix, his long-term teammate at Benfica. He played 20 games as the team form Vila das Aves were relegated in last place, scoring once to open a 2–1 away victory over C.S. Marítimo on 2 February 2020, and being sent off on 11 June in a 2–0 loss at fellow strugglers C.D. Tondela.