Search for "GTA 5 Mobile Prologue v3.0 OBB" on trusted modding forums like GTAInside or GTAForums. Avoid any site with "full version unlimited money" in the title—those are always fake.
No. Rockstar Games has not released a mobile version of GTA 5. This is a fan-made port intended for educational and demonstration purposes. Download Gta 5 Mobile Prologue Version On Android Apk Obb