Finding problem with your raspberry pi that didn’t show properly in monitor? Me too… 😅
I face this problem with my Raspberry Pi 4 when connecting it to my 1366x768 monitor. To solve this problem, let’s start!

The Trick

• Install your OS image (Raspberry Pi OS, Ubuntu, etc) via Balena Etcher or Raspberry Pi Imager from your PC, Mac, or Linux.
• After installing OS image is done remove the microSD/flashdrive/SSD containing OS images and then reconnect it again to PC.
• Open boot partition and look for config.txt file. There is 2 ways to see video output for setting up prefered resolution.
  Choose which you like.
  1. With video safe mode, uncomment #hdmi_safe=1 to hdmi_safe=1.
  2. Output to VGA 60Hz, add hdmi_group=1 and hdmi_mode=1.
• Insert microsd to your raspberrypi slot then boot to system.
• Till you see the desktop,
  open terminal and type /opt/vc/bin/tvservice -m CEA. This will be list for hdmi_group=1
  open terminal and type /opt/vc/bin/tvservice -m DMT. This will be list for hdmi_group=2

For me, in my 1366x768 monitor has DMT result like this :

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Group DMT has 13 modes:
           mode 4: 640x480 @ 60Hz 4:3, clock:25MHz progressive 
           mode 5: 640x480 @ 72Hz 4:3, clock:31MHz progressive 
           mode 6: 640x480 @ 75Hz 4:3, clock:31MHz progressive 
           mode 8: 800x600 @ 56Hz 4:3, clock:36MHz progressive 
           mode 9: 800x600 @ 60Hz 4:3, clock:40MHz progressive 
           mode 10: 800x600 @ 72Hz 4:3, clock:50MHz progressive 
           mode 11: 800x600 @ 75Hz 4:3, clock:49MHz progressive 
           mode 16: 1024x768 @ 60Hz 4:3, clock:65MHz progressive 
           mode 17: 1024x768 @ 70Hz 4:3, clock:75MHz progressive 
           mode 18: 1024x768 @ 75Hz 4:3, clock:78MHz progressive 
           mode 85: 1280x720 @ 60Hz 16:9, clock:74MHz progressive 
  (prefer) mode 87: 1360x768 @ 60Hz 16:9, clock:84MHz progressive 
           mode 88: 1360x768 @ 60Hz 16:9, clock:84MHz progressive

Then I choose mode 87 for optimal value, then I direct edit the config.txt in boot partition. Because I have Caja file explorer, then I open it as super user from terminal with sudo caja and next the opened Caja I can found boot partition easily.
In config.txt, I add following values :

hdmi_force_hotplug=1
hdmi_group=2
hdmi_mode=87
hdmi_cvt=1360 768 60 3
disable_overscan=1

and then restart the system… Voila, I see the optimal video output in my 1366x768 monitor.

This is my experience with Raspberry Pi 4. But it seems that the 2021 release of Raspberry Pi OS has fixed the issue. At least I share this experience that maybe help other who find issue like me. Beside, this tutorial is usefull too to see the available values for your monitor.

After this, thanks for reading this tutorial and see next time… 👍