In 2017 Dunner competed in Spanish F4 for MP Motorsport alongside Bent Viscaal, Christian Lundgaard, Nazim Azman and Marta García.

[9] He was unable to score points throughout the course of the season and finished 27th in the standings, having achieved a best result of twelfth place in the feature race at the Hungaroring.

[13] After almost two years out of the driving seat, Dunner returned to racing ahead of the final round of the 2023 International GT Open, piloting a Mercedes-AMG GT3 Evo at his former EFO team Motopark.

Thereafter, the Austrian competed in all five races of the 2023–24 Asian Le Mans Series season, partnering bronze-ranked drivers Strømsted and Heiko Neumann.

[16] After being joined by Charles Bateman during the first two rounds, Dunner would be partnered by fellow silver-ranked driver and sportscar newbie Lorenzo Fluxá.