What's different between the DX11 and low-spec modes?

[Sawtaytoes]

This game is an incredible graphics showpiece. The fact that it has all these ray-tracing settings and even runs at 60 on my GTX 1080 Ti on my son's PC is phenomenal. For that particular card, I had to put all ray-tracing on low and FSR on Ultra Performance, but it's stable.

I'm curious what the low-spec mode looks like or changes in comparison. I know DX11 is there for compatibility with older cards. It's also going to limit the game to being more single-threaded which helps on some older Intel CPUs. I'm curious what was done to those modes that sets them apart from the DX12 mode other than a lack of ray-tracing.

[TomWheeler]

Feel free to give classic mode a try?
In any case, I'm glad that these different variants exist. On my Elite X2, it crashes on DX12, jerks on DX11 even on the lowest setting, and runs completely smoothly in classic mode. Confusing, but fact.