They deleted almost all missions, audio files, textures, and store interiors .

Modders (specifically credited to ) achieved this massive size reduction by removing almost everything except the "skeleton" of the game :

Large portions of the map were removed, and the entire GTA Online component was stripped away .

Technically, yes, but it is more of a than a fun way to play . It highlights that most of a modern game's "weight" comes from high-resolution art and sound rather than the actual code that makes the game run . Warning: Scams and "Highly Compressed" Files

While it’s not literally a Game Boy game, it is nicknamed "GameBoy" or "PlayStation 1" style because the extreme compression makes the graphics look blocky, low-resolution, and retro . How They Did It

If you are looking for a "highly compressed" version to download on a low-end PC, be extremely careful.