[1] At 14 years, 215 days of age, Santoro won his first medal at a senior international championships, winning the gold medal in the 3 metre mixed synchronised springboard with his partner Chiara Pellacani at the 2020 European Aquatics Championships, held in May 2021 at Danube Arena in Budapest, Hungary, with a final mark of 300.69 points.

[2][3][4] Seven months later, in December in Kyiv, Ukraine for the 2021 FINA World Junior Diving Championships, Santoro started off with a gold medal in the mixed team event on day one, helping achieve the highest mark of 309.95 points.

[5] Two days later, on 4 December, he placed eighth in the 3 metre synchronised springboard final with his partner Matteo Cafiero and a score of 222.81 points.

[11] In July, at the 2022 European Junior Diving Championships in Otopeni, Romania, Santoro won the gold medal in the 1 metre springboard with a score of 478.15, finishing 0.05 points ahead of silver medalist and fellow Italian Stefano Belotti.

[21] On the sixth day, he won a third gold medal in his fourth of four events, scoring 299.25 points with his partner Stefano Belotti in the final of the 3 metre synchronised springboard.