Yes, I did end up finding the Novoton chip. The Linux nct6775 driver identifies it as “NCT6798D or compatible”. It exposes the chassis & CPU fans only, as far as I can tell. The voltages and temperatures are not usable as-is. I’ve only identified 2 of the voltages so far (in0 and in6 are +VCORE_0 and +VCORE_1 respectively, and need to be scaled up by a factor of 9/8.) The temperatures are still a mystery to me, and the numbers don’t make sense—I’m pretty certain that none of my components is 12 degrees Celsius, for example.
The VRM, M.2 and USB4 fans, and the VRM temperatures, can be read off the EC. I created a patch for the asus-ec-sensors module that exposes the fields I was able to identify. See here.