Go to OSX Daily to read How to Dim Flashing Lights in Videos on Mac
It’s not terribly uncommon to encounter flashing lights and strobing effects in videos, and while they can be annoying for most people, flashing light can be particularly problematic for people with epilepsy.
Fortunately, the latest versions of MacOS offer a feature that will detect flashing lights and strobing lights in videos, and automatically dim them. This is a great accessibility feature, whether you’re simply annoyed by flashing lights or if they could cause a health problem.
How to Automatically Dim Flashing Lights / Strobing in Videos on Mac