Forza Horizon 3 runs on the proprietary ForzaTech engine. This engine relies on DirectX 12 architecture, which the PSP hardware and the PPSSPP emulator cannot process or translate.
If you see videos online showcasing "Forza Horizon 3 Android PPSSPP Gameplay," you are witnessing one of two things:
Forza Horizon 3, being a large game, requires specific considerations: forza horizon 3 ppsspp zip file work download work
The only way to play authentic Forza games on a smartphone is through cloud streaming.
If you own Forza Horizon 4 or 5 on a home PC, you can stream the game to your phone for free. Forza Horizon 3 runs on the proprietary ForzaTech engine
If you can tell me (Android phone, PC), I can suggest the best legitimate racing games available for you. Or, I can help you find alternative open-world games that are similar to Forza! Forza Horizon 3 digital download - Microsoft Q&A
Disclaimer: Downloading copyrighted games without owning them is illegal. Always use official, secure sources for your software. If you own Forza Horizon 4 or 5
Emulators are legal. Downloading copyrighted game ROMs/ISOs is a gray area. You are legally safest if you dump your own PSP games using custom firmware.