Some downloads are merely ISO files for the PSP emulator (PPSSPP). However, GTA 5 was never released on PSP. These files are usually just modified versions of GTA: Vice City Stories or GTA: Liberty City Stories with a modded menu screen.
Before you click that download button, consider the real-world consequences:
If you download a file labeled "GTA 5 Android Obb Zip 1.8 Gb" , you will encounter one of five scenarios: