Let’s quickly breakdown the process of anamorphic lenses.
There’s two types of lenses, spherical and anamorphic. Almost all lenses you see are spherical, and project a standard image onto the sensor. However, an anamorphic lens projects an oval shaped image which allows you to capture roughly 2x more horizontal footage. This also means that the aspect ratio is changing.
Back when filmmakers used actual film, anamorphic lenses allowed cameras to capture wider shots, while still utilizing the entire 35mm frame. Basically they could film wider shots, while also enhancing vertical resolution and minimizing grain.