What I was alluding to with regards to idle mclk behaviour is that there are two factors at play: vertical balanking interval (intrinsic to available display modes for each physical monitor) and combined display bandwidth (cumulative of all connected displays to the adapter).

Your mclk will idle high with ‘incompatible’ VBIs, and it’ll also idle high to sustain a lot of display throughput.

This can be observed regardless of GFX vendor, though symptoms may vary somewhat between them. I suppose it could be considered a limitation of GDDR (the same behaviour was never really observed on HBM GPUs like the Vega 64 or Radeon VII)

That said, friends of mine with nvidia gpus have fixed various multi-display specific issues using nvidia profile inspector