Laptop LCD screen flickers and scrambles

Hello community,
I apologise for the long post but I want to describe the problem as well as I can.

The problem:
The screen flickers and scrambles almost constantly. These are my observations and what I tried.

Observations:
- The problem starts before the OS starts to load, right during boot time
- The problem is depending on what picture (or webpage) is the screen displaying (check video Nr.1)
- Sometimes the screen go completely dark or change some colour to another (usually blue to dark green, but not always)
- Everything is absolutely fine on my external monitor, actually if my external monitor is connected the screen on the laptop is more stable (check video Nr. 2). If I pull out the VGA cable the laptop screen goes really crazy (as well as if I start up without the external monitor)
- Also tried to let the VGA in but pull out from the external monitor and the screen also went crazy
- White dotted vertical lines appeared few weeks ago (can be seen to the left from icons), which I didn't pay attention to. Later the flickering started. The white dotted lines are present 95% of time but sometimes they actually completely disappear for few minutes.

Things I've tried:
- I checked the LCD cable which is fine, I pulled it out from LCD and from motherboard, nothing changed
- I tried to push the LCD surroundings but the screen didn't react
- I tried to move the lid but the screen didn't react
- All of the drivers are up to date
- Tried to roll back and reinstall the drivers, but it didn't help

My question is, what could be the problem? The whole LCD? Invertor? Backlight? GPU? Or something else on the motherboard?

Video Nr.1: https://streamable.com/moj1s
Video Nr.2: https://streamable.com/cti0b
Video Nr.3 (bonus): https://streamable.com/2twgp

Please help, any advice would be very helpful
I see the video quality is quite low, I can re-upload them in higher quality if needed