I think that the spoiler is the real thing. Notice the swan neck type mounts leaving the under-surface unrestricted as that is where a lot of the work is done. It is similar to that of the Porsche GT3 RS. The GTD should be a beast. According to Car and Driver, “ Ford's six-figure Mustang features a transaxle, trick aerodynamics, and approximately 800 horsepower”. https://www.caranddriver.com/news/a44840269/2025-ford-mustang-gtd-revealed/