What I was alluding to with regards to idle mclk behaviour is that there are two factors at play: vertical balanking interval and combined display bandwidth.

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 have fixed various multi-display specific issues using nvidia profile inspector