Since San Andreas isn't native to PPSSPP, the best way to play the full content on mobile is through the official ports:
The latest 2024/2025 community builds have pushed the limits of what a PSP ISO can do. Here is what to expect in the updates: grand theft auto san andreas ppsspp highly compressed new
Even with new compression methods, you might face hiccups. Here’s the troubleshooting chart: Since San Andreas isn't native to PPSSPP, the