DLSS is a proprietary Nvidia feature that lets the image be rendered at a lower resolution while making it not appear as degraded as would normally be the case.

https://en.wikipedia.org/wiki/Deep_learning_super_sampling

Deep learning super sampling (DLSS) is a family of real-time deep learning image enhancement and upscaling technologies developed by Nvidia that are exclusive to its RTX line of graphics cards, and available in a number of video games. The goal of these technologies is to allow the majority of the graphics pipeline to run at a lower resolution for increased performance, and then infer a higher resolution image from this that approximates the same level of detail as if the image had been rendered at this higher resolution. This allows for higher graphical settings and/or frame rates for a given output resolution, depending on user preference.

I expect that the mod enables that functionality and that the modders is charging for it and that people who don't want to pay for it are pirating it.

From what I've read, Starfield generally performs better on AMD cards, so I imagine that there's particular interest from Nvidia users in figuring out some performance tweaks.