Question: My display is a TV with resolution of 1366x768 @60 Hz. It has HDMI input option as well as PC input option. I prefer HDMI input but I'm not getting the appropriate image of RPI 4B with 4GB with HDMI. I borrowed a monitor and found that display is excellent without me doing any configuration from the RPI 4B. I'm a noob and could not set it correctly on my tv with built in screen configuration tool of RPI 4B. When I set 1366X768 resolution my TV first shows a message 'unsupported' but after about a minute the display comes on the screen which is not the best. I ran tvservice and got the following best score by GREP:
HDMI:EDID Best score mode is now DMT (81) 1366x768p @60Hz with pixel clock 85 Mhz (score 5188835). I'm confused about DMT and CEA as I read somewhere that DMT is intended for monitors while mine is a TV. Even if DMT is the right option I need step by step guidance on how to set my TV display to DMT 81. Please help. (I've very little knowledge of linux commands but I'll be able to follow a detailed guidance).

Answer: 
You could try 720p mode as you have a Pi 4:

Full config details are [here on the RPF site](https://www.raspberrypi.org/documentation/configuration/config-txt/video.md).

Add the following lines into /boot/config.txt

```
hdmi_group=1
hdmi_mode=69

```

and restart the computer.

Edit:
To use dmt add:

```
hdmi_group=2
hdmi_mode=81

```

and restart the computer
Kind of late, but perhaps could help others looking for solution to the same problem as it did
help me.

Short answer, put these commands into config.txt:

```
hdmi_drive=2
hdmi_group=2
hdmi_mode=87 
hdmi_cvt=1360 768 60

```

The `hdmi_drive=2` is to run audio through HDMI. You also may need to add these and possibly other commands,
check config.txt documentation link below.

```
hdmi_force_mode=1
hdmi_force_hotplug=1
hdmi_ignore_edid=0xa5000080

```

Long answer, Pi 4B doesn't support 1366x768@60 mode, but it supports 1360x768@60 which may work for you.
But you need to set it manually. From <https://www.raspberrypi.com/documentation/computers/config_txt.html>:
"The Raspberry Pi 4 can not support a timing where any of the horizontal timings are not divisible by 2. The
firmware and Linux kernel will filter out any mode that does not fulfill this criteria.
There is only one mode in the CEA and DMT standards that falls into this category - DMT mode 81, which is 1366x768 @ 60Hz