I had some difficulty getting my dual 1440p displays working on my Raspberry Pi 4 8GB model, so I thought I would document my solution for others. This is assuming you are using Raspberry Pi OS.
The following lines in /boot/config.txt worked to get a single 2560 x 1440 display working at 50hz:
# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=2
hdmi_mode=88
hdmi_cvt=2560 1440 50 3 0 0
And this setup worked for dual 1440p displays:
# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=2
hdmi_mode=88
hdmi_cvt=2560 1440 50 3 0 0
hdmi_group:1=2
hdmi_mode:1=88
hdmi_cvt:1=2560 1440 50 3 0 0
Background:
For some reason the usual configuration GUI would show 2560 x 1440, but when I selected it the screen would go black.
I have two Monoprice 27" 2560x1440 displays.
I think it is model 110489, but no longer sold:
https://www.amazon.com/Monoprice-110489 ... B00CE2T19I
https://www.anandtech.com/show/7415/mon ... cd-monitor
It appears to be able to "overdrive" up to 75hz, but 60hz (or 59.94hz true) is standard. But I cannot seem to get them working beyond 50hz. This is fine for my needs though.
I finally discovered the solution by experimenting with raspi-config after adjusting the config.txt file in various ways. That is how I discovered mode 88, which seems to be the key.
Note that I tried 60, 59.9, and 59hz, and none worked. 30 works fine, and then I tried 50 and it worked.
Note that the :1 (e.g. hdmi_group:1) is for second display. :0 is assumed for primary, but I suppose you could specify it.
Reference:
https://www.raspberrypi.org/documentati ... t/video.md