WhiteWolf
It is a known issue with AMD GPUs (both on Linux and Windows).
Long story short:
With 2 monitors connected you will pretty much always get max memory clock (especially if there is a big difference in refresh rate and resolution between the two) to avoid problems according to AMD.
For single monitors AMD blames the monitor manufacturers and their "non standard timings" that won't allow the memory to clock down. And depending on your monitor messing with the timings either via custom resolutions or editing the monitor EDID does actually fix it. Reducing the refresh rate might also help.
Setting my 75Hz monitor to 60Hz on a 5700XT fixed it for me on Linux. On Windows I edited some of the monitor timings via CRU and that also fixed it for 75Hz.
If I only have my 120Hz connected it clocks down properly on Windows too without having to mess with timings.
It is a combination of intended behavior from AMD, bugs and depends on the monitor you are using (and it sucks).
I guess they broke it again on 5000 series cards.
But another fix might be coming soon (at least for 6000 series cards).
https://gitlab.freedesktop.org/drm/amd/-/issues/1403
