Mortal Kombat X was never officially released for the PSP, meaning

Risks and typical issues with unofficial PPSSPP builds

• Legal risk for downloading copyrighted ISOs.
• Malware and bundled unwanted software from shady download sites.
• Broken or incomplete game assets, crashes, missing textures, or audio.
• Savegame incompatibilities and corrupted progress.
• Poor performance on lower-end Android devices.

If you're looking for an official, high-fidelity experience designed specifically for mobile hardware: Mortal Kombat Mobile - WB Games

So if you want the real MKX experience on Android via PPSSPP, it doesn’t exist. But if you want the closest possible MK game (MK Unchained) or a heavily modded version, follow below.