Why is my whole screen flashing blue (not a notification light)?

[AC Question]

My screen has started making a blue flash each time I get a notification two days ago. It did not do this before. I don't have an LED notification light, so please don't tell me that's what it is. There is no option under Display for LED. It's the whole screen that turns blue briefly. It's for all notifications, not specific to any one or type.

 

[the tall guy]

Hi, boot your device into safe mode and see if it still happens. If it doesn't then the issue is being caused by a 3rd party app you've installed.