“Software rendering” usually means “doing rasterization on the CPU”, as opposed to “hardware rendering” that is done by the rasterization primitives of the GPU.

Nanite is a bit weird because it doesn't use the hardware rasterization of the GPU, but it's still doing rasterization on the GPU, so it doesn't really fit this dichotomy.

No software rendering requires DOS, you could use it with Windows back in the day (how I originally played Half Life) and engines that still support it will run on modern OSes too.

Its probably not correct to state this. Its probably a combination of how nanite itself is doing Lob, lightning etc.

A mix of software and gpu

Eh, Nanite rasterisation is still happening on the GPU, it's "just" implemented in shaders rather than using the fixed-function pipeline. "Software rendering" is becoming less useful as a descriptor as graphics hardware becomes more general.

At this point words get blurry. Is using CUDA or a compute shader "software rendering" or not?