The original game was designed for 4:3 CRT monitors. Without these files: The image is , making CJ look wider than he is. The FOV (Field of View) is cramped. The HUD elements (radar, weapon icon) become oval-shaped.
To get running in crisp 1080p (or even 4K), you generally need a community-made patch, as the original "vanilla" PC release lacks native support for modern widescreen resolutions. gta-san-andreas-1080p-resolution-fix-file
If you experience weird physics (like cars not reversing or swimming being impossible), ensure the Frame Limiter is ON in the display settings, or use SilentPatch to cap it at a stable 60 FPS. The original game was designed for 4:3 CRT monitors
Using the ThirteenAG Widescreen Fix corrects the aspect ratio and scales the interface perfectly to 16:9 or 21:9 monitors. you generally need a community-made patch