I notice you're asking for an ISO file for to run on PPSSPP (a PSP emulator).
If you simply want a console-style open-world racer on PPSSPP, here are that exist and run beautifully: forza horizon 4 iso file for ppsspp patched
: Some "patches" are actually just save files that unlock all cars and max out currency in a different racing game to mimic the Forza experience. I notice you're asking for an ISO file
No legitimate "Forza Horizon 4" PPSSPP ISO exists. The Reason: Forza Horizon 4 was released in 2018 on Xbox One and PC. The PlayStation Portable (PSP) was released in 2004 and discontinued long before this game was developed. The hardware is incapable of running the actual game. forza horizon 4 iso file for ppsspp patched