I've got the Sapphire Nitro+, removed WEG, disabled iGPU, and I got it going. BUT I seem to be able to only use the 2 HDMI ports on my card. Going DP out from the card to DP in on the monitor seems to produce a black screen.
UPDATE: got the DP working with WEG installed with boot argument agdpmod=pikera added. However, not I have obnoxious red lines/artifacting on desktop. May need to wait for an update to WEG
UPDATE 2: Interesting...the red lines only appear when I am using the Catalina or Mojave dynamic wallpapers, OR any of the still wallpapers that make up the Catalina and Mojave dynamic wallpapers...the Solar Gradients dynamic wallpaper and any other stills dont display any red lines/artifacts...weird.