(In reply to Peter Weber from comment #8)
> The DP of the RX 560 works fine at 3480x2180@=
;60Hz, but via HDMI it fails
...
> HINT: Don't used "DEEP COLOR" (LG OPTI=
ON for 8/10BIT COLOR?) with HDMI or
> everything is busted, but that is a minor issue, as for now.

Do you realize that LG's "deep color" option for HDMI ports essen=
tially means
that only if this option is enabled, they support >300MHz signals on tho=
se
inputs?

To allow for 4k 60Hz modes, you will need to enable that "LG deep colo=
r" option
on the respective input, otherwise you cannot expect 4k 60Hz to work - it d=
oes
require up to 600Mhz signals.

If with "LG deep color" on you do get 4k 60Hz output, but distort=
ed, you might
want to try better/shorter HDMI cables, as many HDMI cables (and especially
every cable over 5 meters length) do not conduct 600MHz signals with suffic=
ient
quality.

The issues with the amdgpu driver is just that it does not even offer to en=
able
4k 60Hz modes if some bit in the GPU's bios seemingly indicates insufficient
support for such, but this bit seems to be bollocks for several GPU brands =
and
seems to be rightfully ignored by Windows drivers.