Okay, this is now my third or forth attempt at getting Eyefinity to work with PLP. I am going to try to give as much details as possible that maybe it can finally get working properly.
I am running an all-AMD rig; Threadripper 3960x with 32GB of DDR4-2066 paired with a bone-stock/reference Radeon VII. I am running Windows 10 Pro on a 2TB Western Digital Black NVMe drive and Radeon Software version 20.4.2. I had problems getting PLP to work right on my Intel/Win7 rig, hence the change.
My main monitor is a 55" LG UK6090PUA (4096x2160 native IPS TV) routed though a Marantz SR6014 with the newest firmware available. On either side of that is an Acer EB321HQU running in portrait mode, with custom resolutions set of 2160x1260, which means when in portrait mode, all three displays have a vertical resolution of 2160. Using only display fusion, my regular desktop experience is beautiful:
Desktop view: https://i.imgur.com/eS47vU9.jpg (a bit janky looking due to bezel correction)
Actual view: https://i.imgur.com/4nwbElo.jpg
This is great, but you cannot game on three monitors as is. I used to use SoftTH, but that doesn't seem to work in Win10, and its fewer and fewer games that are Dx9 anyway, so I need to go Eyefinity. I try to set it up, and the only option I have is to hit enable in the control panel, and let it figure it out on its own. (I found how to adjust bezel correction, but that's not the big issue here...)
Desktop view: https://i.imgur.com/tbv9SIb.jpg (great, so far so good)
Actual view: https://i.imgur.com/aK8mPng.jpg
The heck? I double check the AMD control panel, and sure enough, monitor scaling is off. Enabling it seems to do nothing; whether I select preserve aspect, full panel, or center, it makes no difference.
On the monitors themselves, I've tried 1:1, Aspect, and Full, and it also makes no difference to the image shown on the display.
The main display is connected with an active DP=>HDMI adapter into the HDMI input of the Marantz, which then goes into the HDMI of my LG. The two side displays are connected with native DP to DP.
What the heck am I doing wrong? Why can't I get this to work right?
For sake of completeness; I just tried installing 20.8.3; no better.