I own a laptop with a Ryzen 4800H and RTX 2060 and I’m also in the same situation as you. The (fine-grained) mode doesn’t work and shows Runtime D3 status: Not Supported. The (coarse) mode works just fine, like yours.
It seems that maybe we out of luck, because I saw this comment and the guy in that thread have a Ryzen 5900H and /proc/driver/nvidia/gpus/0000:01:00.0/power shows Runtime D3 status: Enabled (fine-grained).
I decompiled my ACPI tables and shows the _PR0 and _PR3 methods but still it doesn’t work with my 4000s series Ryzen. It could be that maybe there’s something in the latests Ryzen 5000s series that add support to RTD3 or maybe the nvidia driver excludes most of the Ryzen mobile APUs. But that is something that a Nvidia developer must clarified