Red Dead Redemption 2 (RDR2) was for the PlayStation Portable (PSP). Any files claiming to be a "PSP ISO" for RDR2 are either fan-made mods of other games (typically Grand Theft Auto ) or malicious software. The Reality of "RDR2 PSP ISO"
For the best outlaw experience, stick to the official releases on PC, PlayStation, or Xbox, and use remote streaming to get your fix on the move.
They typically require specific Save Data and Texture packs to be moved into the PSP/TEXTURES folder of your emulator. 2. PC-to-Handheld Streaming