r.DetailMode is affecting shadows, I'd like to know how.

When I change r.DetailMode=2, my shadows have ambient lighting.
When I change r.DetailMode to anything below 2, the shadows are completely black.

I’d like to know what is actually being changed in terms of shadow/light settings.

What are the settings being affected when DetailMode=2? I imagine DetailMode is an ambrella setting that changes a lot of settings, how can I only change the setting(s) that affect the shadows - as in below images?

2 hours of trying to find it, and I find an answer 15 min after posting the question.

The problem was that SkyLight was being turned off in DetailMode=1, it worked once: