Many small dots on the screen after heating/usage

I've got a lot of small dots on the bottom part of my screen. When you turn on the laptop they do not exist initially but after usage they start to appear. It might be me but it seems that heating plays a big role here.

• I have reseted NVRAM - does not help.
• Ran Apple Diagnostics - it detected nothing.

Has anyone ran into this issue before?

What's the best way to act here or solution?

Macbook Pro is 5 years old and the screen has been replaced once. ( 4 years ago )

Specs:

MacBook Pro (Retina, 15-inch, Mid 2014)

2,5 GHz Intel Core i7

16 GB 1600 MHz DDR3

Intel Iris Pro 1536 MB / NVIDIA GeForce GT 750M