I will not give steps for:
Legitimate "repacks" (compressed game installers) exist from groups like FitGirl, DODI, or ElAmigos. However, even their best compression keeps GTA 5 around 35GB to 45GB. They achieve this by: Gta 5 Highly Compressed 100mb For Pc
But 35GB is still 35,000MB. That is 350 times larger than the 100MB you are searching for. Scammers use the term "100mb" purely as clickbait for search engines. I will not give steps for:
GTA 5's actual size is around 72–105 GB (depending on version).
A 100MB compressed version is mathematically impossible without deleting 99.9% of game files (no textures, audio, maps, or missions). But 35GB is still 35,000MB
Any website claiming "GTA 5 100MB PC" is either:
Downloading such files risks: