I upgraded from Geforce GTX 1050Ti to Radeon RX580. Basic reason was to get better performance from X-Plane 11 in Steam.
I also upgraded CPU from Ryzen 5 to Ryzen 7.
I then did a complete reinstall of Manjaro KDE.
I am happy with the performance of the Radeon RX580. However, one feature of the GTX 1050Ti that was enormously satisfying was the 'Xinerama' setting that allowed me to combine my three monitors into one large monitor. It took much research to get Xinerama to work. There seems to be very scanty/confusing documentation about getting Xinerama to work.
What did work was changing this line in the '90-mhwd.conf' file (if I remember the name of the file correctly):
Option "Xinerama" "0"
Option "Xinerama" "1"
I then would restart 'sddm' with this command:
$ sudo systemctl restart sddm
After this restart, my 3 monitors acted as one large monitor.
Flying X-Plane 11 in Steam was marvelous with 3 monitors. But the graphic performance was sub-optimal even with the GPU and CPU overclocked.
I want to be able to achieve the same result with the RX580 of combining all three monitors into one large monitor.
I have searched for days, but have found no clear, or even closely-related answer.