[8] In 2019, Nielsen stepped into the LMGTE category, driving for Luzich Racing in the European Le Mans Series and partaking in the 2019–20 FIA World Endurance Championship campaign at AF Corse.

[11] During the WEC campaign, one that Nielsen contested alongside François Perrodo and Emmanuel Collard, he finished third in class at the Le Mans 24 Hours, on his way to win the title with two victories and five podiums to their name.

[12] Having been promoted to FIA Gold ranking ahead of 2021, Nielsen returned to the WEC's LMGTE Am class with AF Corse, partnering youngster Alessio Rovera and gentleman driver Perrodo.

[18] The same season also saw Nielsen triumph at the 24 Hours of Spa, in a performance which helped him, Alessandro Pier Guidi, and Côme Ledogar to take home the GT World Challenge Europe Endurance Cup championship.

[19][20] For the 2022 season, Nielsen moved into prototype racing, competing in the LMP2 category of the WEC and ELMS respectively, remaining with AF Corse, Rovera, and Perrodo in the series's Pro-Am subclasses.

Nielsen, Fuoco, and Molina managed to beat their sister car in the standings, despite the latter winning the Centenary Le Mans, a race in which the #50's hopes of victory were dashed due to a radiator leak during the night.

Having managed his car's so-called virtual energy tank during the final thirty minutes, Nielsen crossed the line in first place, earning him, Fuoco, and Molina their first ever overall victories at the Sarthe, as well as defending Ferrari's Le Mans crown from the previous year.