Netflix brightens the screen when subtitles appear. what's the matter?

Question

safari

Hello, on my macbook, when viewing in safari netflix in full screen, the following problem is observed:
When subtitles appear, the screen becomes brighter a little, as soon as the subtitles disappear, the brightness becomes normal, then the subtitles again and again the brightness is slightly higher. I would not say that it becomes very bright, but this constant disco is already tired. the problem cannot be in the macbook. I had the same problem on my iMac earlier. what's the matter? who faced?