There was a patch that’s fixed the PC version so now I can turn on RTX without crashing.
It does look very good with the global illumination turned on, although as with Cyberpunk 2077 the real time reflections are so expensive it’s just not worth it. With GI I’m getting around 50-60fps with ultra settings at 1440p (DLSS balanced), which is smoothed out quite nicely by the VRR. So basically it’s very playable. There are still occasional stutters though.
Here is the DF rundown as well. Does a good job of explaining the improvements that the global illumination make to the world and why it looks so much better here than the default lighting implementation (the default lighting has some weird limitations).