While the full game is massive, some legitimate "repacks" (compressed versions) exist, but they are still far larger than 100 MB:
In the world of data science, there are limits to how much information can be compressed. Standard compression tools like WinRAR or 7-Zip can reduce file sizes significantly, but shrinking a game of this magnitude by 99.9% is technically impossible without losing vital data. download gta v highly compressed 100 mb for pc full