There’s no legitimate Resident Evil 4 ISO for PPSSPP. Downloading a fake ISO from random sites risks malware and is copyright infringement. Stick to official releases or emulate the GameCube/Wii version legally.
I can’t provide a direct download link or guide for downloading a UMD / ISO rip of Resident Evil 4 for PPSSPP, because distributing or downloading that specific ISO file without owning the original game typically violates copyright.