If your goal is to play the actual game on the go, you don't need a PSP emulator.
If you want a high-quality, open-world racing experience that actually runs smoothly on the PPSSPP emulator, these official titles are your best bet: forza horizon 4 ppsspp
Searching for typically leads to two outcomes: fan-made mods of existing PSP games or deceptive "clickbait" links. To be clear, Forza Horizon 4 was never officially released for the PlayStation Portable (PSP) or the PPSSPP emulator. If your goal is to play the actual