Picture (video) jumps from bright to dim

Depends on the model. Have you checked the backlight, (LED in this set perhaps).

https://www.youtube.com/watch?v=BX45RuQnGuY
I dug around in the settings, searched the web, and finally figured it out. On my TV-Vizio D32-D1-the setting is: Menu > Picture > More Picture > Backlight Control. Set Backlight Control to Off. There's also Menu > Picture > Auto Brightness Control which I switch off as well for good measure
https://it4np.com/2019/07/vizio-tv-picture-keeps-dimming-and-brightening-on-its-own-solved-fixed-.html

Your circuit lights may be bright or dim according to how your electrical system was set up. It may dim when lights are off and get bright when lights are on. ------------------------------------------------------------------------------------------
Car Diagnostic Tools

The led backlights may be failing or the driver circuit isn't working. TV Parts Universal TV Stands DLP Chips ShopJimmy You can get parts and led testers here.

The part you need is called a CCFL Backlight. Basically, there are lights in the screen that back-light/illuminate the display. Over time it burns out and you are left with a dim and completely dull display. These are a pain to replace and expensive when bought from the manufacturer. But this site has a break down with dis-assembly instructions...if you want to try it.

Press and hold the 'FN' key and tap the key that has the picture of a sun and an up arrow (or some other similar picture that dictates brightness - there should be two different keys that affect brightness one to increase and the other to decrease). Once you have the brightness set to your liking quit tapping the 'brightness' key and release the 'fn' key

You could have a defective screen - a defective inverter or a CCFL lamp.
To determine if you have a LCD screen or video card problem, read this and follow the instructions.

Defective CCFL backlight, it may have the following symptom:

• Screen flashs on red/pink and off.
• Picture stays on in red and slowly be come normal.
• Picture flickering with dim display.
• Picture flickering on and off.

All these symptoms indicate that the LCD backlight lamp (CCFL Lamp) has reached the end of the life and all you need to do is replacing the CCFL lamp

Connect an external monitor to your laptop and power it up, if you see the normal Windows images then the video card and laptop is OK and the problem is definitely the backlight.

Dim image and/or dark display on the laptop's LCD screen indicates a faulty LCD backlight and it could be the inverter that supplies high voltage to the CCFL lamp or it is the CCLF lamp is nearly burnt out or burnt out, most likely this is the case.
The inverter can be replaced easily but the CCLF lamp is more time consuming and requires soldering skills.
Check out www.lcdparts.net for parts, repair service and DIY info.

This is probably normal and called "Dynamic Contrast". Maybe this company has some other proprietary naming.

Basically, the Backlight (LCD) or Bulb (Projection) will be dimmed during dark scenes to allow the TV to make a deeper black.

Does it go completely black or just dim? Most displays dim when you turn the lights on to make the display darker so its not too bright. GPS and other displays do this. Do you have any problems with any other of the car's electronics?

sure, lcd tvs need to be tweeked depending on the light in the room the darker the worse the picture. so try this
from standard:
picture: 85 to 95 %
brightness: 45% or adjust the black of the video to the black of the pilar bars to equilize them.
color: 32 to 38% or until the flesh tones are not so hot
sharpness: low 10%
tint: always to center
color temp: cool1
back lamp ( if avalible) low when lights are dim, high when lights are bright.
the problem with LCD is they don't look so good with dark sceens. the contast ratio is very low. natively 3000:1 aas compaired to plasma or other direct view TVs. the LCD is back lite and the thin materal of the LCD can not completely block the back light from coming thru. there for the complete "black screen" is illuminated "blue". the best thing is to keep the lights on bright in the room for the best picture.