Since after High Sierra (Mojave I think?), Apple eliminated the ability to use non-metal drivers on macOS wholesale. Nvidia’s drivers weren’t developed in Metal and there’s zero reason for them to do so (only way to use Nvidia is intentionally either as an addon to a Mac Pro or as an eGPU, which they don’t see a large market for it) and Apple has a long history of killing off support of something on their platforms, users be damned.