Like said in the title, it would be super cool to have some flash effect when lightning strikes close to the player, but can be even when it's further like creating 4 distances giving them certain brightness. Maybe some effects that you can get would be cool. By the brightness, just white overlay can work, but it would look better if you could apply the brightness to the surroundings (to mimic irl behaviour, but idk really how hard and possible it is).

In addition, if some explosion or lightning (or anything that is supposed to be loud) occurs, you should get effect "deafness" which will make you lose partially your hearing senses (muffled sound or not hearing at all, then linearly getting the hearing back).

Sorry, but I'm not really able to do something like that. It would require good knowledge of shaders, which I do not have.

Sorry, but I'm not really able to do something like that. It would require good knowledge of shaders, which I do not have.

I understand. However there are other ways too. Just some white filter would be better than nothing. Making contrast as low as possible, then setting the value back. The opacity will depend on how close the lightning is. In fact I had this idea while trying and setting this mod:
https://www.youtube.com/watch?v=OmK9YXnVWdI
In short, it makes the sound of thunder more muffled and less loud depending on how distant the lightning is. Depending again on the distance should be changed the opacity of those filters. It can be contrast, it can be brightness, it can be white filer or just white overlay, this is up to you.

You also need shaders to adjust contrast etc.
Sorry but for the moment I do not have the time. Maybe at some point in the future.