If you were to put /effect give @p minecraft:blindness 1 0 true into an always active repeating command block, it will result in rapidly flickering screen. Since the effect is still active for a short period of time right after the blindness fades away, it will result in the rapidly flashing screen shown in the video link below.

While I am not epileptic myself, it still hurt my eyes to look at the flickering screen for more than a few seconds. So, do not watch the video if you are prone to epileptic seizures. ou7d3h.mp4

A possible solution maybe is that the blindness effect only fades away after the blindness effect is no longer active on the player, instead when there is less than a second left.

The same problem applies to the night vision effect (via /effect give @p minecraft:night_vision 10 0 true), see [MC-206109] - Minecraft 1.19 Pre-Release 2 (Epilepsy Warning).