Flashing bar on Macbook Air screen?

[deedeerotten]

Hi! Has anyone seen thins kind of flashing bar on Macbook Air screen:

I haven´t dropped the device on the floor or anything. Specs:

Macbook Air 13" 2017
macOS Catalina 10.15.6
Intel HD Graphics 6000, 1536 Mt

Thx 4 advice!

 

[deedeerotten]

Update: Changing resolution does not solve the problem. BTW, the bar is not visible when I use external monitor.