[2] Fittje competed one race in the 2019 Porsche Mobil 1 Supercup for Team Project 1 - Fach in Spain where he recorded one point by finishing 16th.

For the 2022 season, Fittje joined Haupt Racing Team to compete in the Silver Cup of the GT World Challenge Europe Endurance Cup alongside Jordan Love and Alain Valente.

[3] The team failed to score any points in the main championship whilst taking tenth place in the category standings.

During 2023, the German teamed up with Antares Au, Matteo Cairoli and Tim Heinemann in the Bronze Cup for the 24 Hours of Spa.

[4] This would prove to be a resounding success as Fittje, having seen Cairoli take overall pole position, helped his outfit to a class victory, which he later called "the biggest and best result" of his career.