The PSP console was discontinued long before MK11 was developed. When you see these files online, they are almost always highly modified versions of older games (like Mortal Kombat Unchained or Mortal Kombat Shaolin Monks ) that have been "modded" by fans to look like MK11.
Since these are unauthorized fan mods, they can be unstable. If you use the PPSSPP emulator, use the "Savedata" feature often, as these modified ISO files are prone to crashing during "Fatalities" due to the high memory usage of the injected graphic assets.