Juniors Kapp had a successful junior career, skipping the German national junior men's team at three
World Junior Curling Championships, and is a
2022 and
2023 silver medalist. Kapp also skipped the German mixed team at the
2020 Winter Youth Olympics, finishing 8th after losing to New Zealand's
Hunter Walker 7–4 in the quarterfinals.
Mens While a still of junior age, Kapp would be the alternate on the German men's national team at the 2019 and 2023 editions of the
European Curling Championships, and the 2022
World Men's Curling Championship. Kapp would join as the third of the new German team skipped by
Marc Muskatewitz during the
2023–24 curling season, alongside junior teammates
Felix Messenzehl and
Johannes Scheuerl. The new team would have a strong showing at the , finishing in 5th place after losing to Italy's
Joël Retornaz in the playoffs. However, the team would build upon this success at the
2024 European Curling Championships, they would beat Scotland's
Bruce Mouat 9–7 in the final to win Germany's first European medal since 2008, and their first gold since 2004. After winning the European Championships, the team qualified for their first Tier 1
Grand Slam of Curling event, the
2024 National, where they had a strong showing, losing in the quarterfinals to
Mike McEwen 6–5. The team also continued to perform well on the world curling circuit, winning the
2024 Karuizawa International Curling Championships. Muskatewtiz would then win the 2025 German Men's Championship against
Sixten Totzek, qualifying the Muskatewitz rink to represent Germany at the
2025 World Men's Curling Championship. At the 2025 World's, team Muskatewitz would finish the round robin with a 5–7 record, finishing outside of the playoffs in 8th place. However, the Muskatewitz rink's performance over the last two world championships earned Germany enough points to qualify directly for the
2026 Winter Olympics. ==Personal life==