The 55NANO786QA is a 55 inch 4K TV from LG, launched in the year 2022. It comes with a 10-bit VA panel.
It can achieve a max resolution of 3840 x 2160 @ 60 Hz with a pixel density of 80 ppi.
Picture Quality
After screen size and resolution, the next most important feature to look for in a display is its Color Reproduction Accuracy, which is defined by its color gamut specification.
This TV doesn't provide a color gamut specification, so we have to make an assumption based on its panel type.
Now, since the TV features a 55 inch screen, it won't come with a cheap panel, so here we can assume its equivalent sRGB coverage to be 90-100% or above. Undoubtedly The color accuracy on this TV should be Lifelike! It will produce color accurate images.
Understanding Color Gamut
Color gamut specification of a display is a measure of the range of colors that the display can display.
What this means is, this specification determines the ability of a TV to produce accurate colors. A TV with low color gamut coverage will miss out on some colors (such as deep red), the result would be a "washed out" picture quality.
It is specified in different units - sRGB(most popular), NTSC 1953, DCI P3 Adobe RGB, rec.2020. It is upto the manufacturer which one they choose.
But you don't need to worry about that, here is a chart that you can use to choose a TV with good color accuracy.
After color gamut, the static contrast of a TV also impacts its picture quality.
What is Static Contrast ?
A TV with low static contrast ratio will not produce deep enough blacks and possibly can bleed backlight as in the below image:

The static contrast ratio of above TV is rated 800:1. So make sure you get a TV with a static contrast of >= 1000:1. Ofcourse, More the better.
Other than black levels, a TV with high constrast ratio allows you to see more details. So, resolution and static contrast ratio go hand in hand in a sense.
If given a choice, I will prefer a FHD TV with high contrast ratio over a 4K TV with low contrast ratio.
There's no mention of this spec in the TV's official specsheet. So once again we have to take a guess based on the TV's other specifications. The static contrast ratio of this TV would be surely atleast 3000:1. As you know, this TV comes with a VA panel, these panels by nature have high contrast ratios.
HDR is also supported on this TV in form of HDR10 Pro and HLG (Hybrid Log Gamma).
As for brightness, the peak luminance the TV can produce is 250 nits. The backlight of this TV is powered by Direct LED technology.
Gaming Performance
Now if you are planning to use a TV other than using it as a TV — say as a PC monitor or Gaming, you should take a TV that features the lowest input lag. For gaming however, both input lag and response time affects the performance.
Unfortunately, we cannot find the input lag specification for this unit. But as this is not a cheap TV from LG, we can expect an input lag of less than 20ms.
What is Input Lag and Why it matters ?
This lag is the latency at which device inputs changes the content of the screen. For casual Non-FPS games, input lag doesn't matter much.
For best of both worlds, get a TV that comes with an input lag and response time of < 20ms.
Ergonomics and Dimensions
Coming to ergonomics — If you plan to wall mount the TV, you can make use of the VESA mount provided with this TV, which by the way has an interface size of 300 x 300 mm. The unit doesn't come with Swivel, Tilt or Pivot support.
The TV measures 55 inches vertically and 48.62 inches horizontally.
It is 2.29 inches thick.
Overall it weighs 16.0 Kgs including stand. Without stand, it weighs 14.6 KGs.
Hardware and Audio
The TV comes with a Quad Core CPU. There is no data about the RAM on the TV's official specsheet.
To power its UI, the TV runs webOS 22 Operating System.
For display connectivity, there are three HDMI 2.0 ports on this TV.
For connecting USB devices, you will have two USB 2.0 ports. Other connectivity ports include — 1x Satellite In (F-type female), 1x Antenna (RF) (female), 1x CI+ 2.0 and 1x Ethernet RJ45.
Regarding wireless connections, the manufacturer has provided a 5Ghz Wi-Fi, 2.5 Ghz Wi-Fi, Wifi-Direct, Bluetooth 5.0 and DLNA.
The Audio unit of this TV is powered by 2 x 10W speakers.
Now, coming to power consumption, the TV consumes 84W on average and 0.5W on standby.
Both 110V and 220V outlets are supported on this unit.