Extract your ZIP once, then if needed, convert ISO → CSO using YACC (Yet Another CSO Compressor) on PC, or within PPSSPP (long-press ISO → Convert to CSO).
If you find a .zip online (for backup purposes): ppsspp gta san andreas zip file download android better
You are looking for a file size between . Anything smaller than 500MB is likely a fake texture pack. Anything larger than 2GB is probably a PC game mislabeled. Extract your ZIP once, then if needed, convert