To play Resident Evil 4 on PPSSPP, you'll need to install and configure the emulator. Here's a brief guide:

This isn't a stripped-down "mobile" game in the modern sense; it is a full campaign. You get the complete story of Leon S. Kennedy's mission to rescue the President's daughter, Ashley.

Some modders provide custom HD Texture Packs that can be loaded within the PPSSPP app to improve character models and environments. How to Play Using PPSSPP

In 2009, Capcom released a bizarre Java-based version of Resident Evil 4 for flip phones (iOS Classic and Zeebo). Modders have since converted this version into an ISO that runs decently on PPSSPP.