Is 16GB of RAM critical for a build with an i3-13100F and no dedicated GPU?

Yes. With an i3-13100F and no dedicated GPU, you’re relying on the CPU’s integrated graphics (UHD 730), which borrows system RAM for video memory. 8GB total leaves only 1–2GB for the OS and game, causing stutter and frame drops in GTA V at 1080p low. 16GB gives the iGPU 2GB for video memory and leaves 10GB+ for the game, making the difference between “playable but annoying” and “actually enjoyable.” Don’t try to save $30 here—get 16GB.