I have the same problem, but with the MSI Evoke 5700 XT. If yo=
u read
/sys/class/drm/card0/device/pp_dpm_mclk you should find that it's forced to=
 the
highest state (3: 875Mhz) and that although it lets you set a lower value, =
it
immediately jumps back to the maximum value.

In theory, this problem should have been fixed with
b90053edc9d6d639ddb600f8799d990d92aca328 in amd-staging-drm-next:
drm/amd/display: Support uclk switching for DCN2

but it doesn't seem to fix the problem for me. Before this, you could revert
the old workaround:
02316e963a5a drm/amd/display: Force uclk to max for every state"=20

and you could manually set mclk.

I should note that from some brief tests on Windows, the card also seem to =
be
stuck at maximum mclk (it's actually even worse since temperature readings
don't even work there). So it could be that aftermarket cards need some ext=
ra
work, in order to work properly.

System:
Mesa git
amd-staging-drm-next (also tested 5.3-rcX and drm-next-5.4)