Modders create "Lite" versions (often around 200MB–400MB) by removing all radio stations, cutscenes, and lowering texture quality. A version as small as 50MB would likely lack essential files needed to even start a mission.
Many sites claiming to offer 50MB versions provide files that contain malware or are simply "clickbait" that leads to endless surveys. Minimum System Requirements gta san andreas android highly compressed 50mb
The official Grand Theft Auto: San Andreas on Android typically requires about of storage space. Compressing this down to 50MB (a 98% reduction) is technically impossible without removing core components of the game. gta san andreas android highly compressed 50mb