What do i do wrong ?

Toast

I make baguette dough with 76% hydration.
I mix all the ingredients, let it rest for an hour, then do stretches and folds and coil folds,
i do it every 30 minutes and 4 times, but still the dough is too sticky and i can't work with it properly
and can't shape it properly.
How do i solve this ?

You didn't say what kind of flour you used, but the most likely solution is to reduce the hydration until you can handle the dough.

No matter what a given recipe says, some flours are very touchy about how much water you can use with them.

TomP

white flour, which is said to be suitable for making pizzas and focaccias, 

and it contains 12 grams of protein per 100 grams of flour.

Is it strong enough ?

"White flour"? Hmm, what country is it from? It's got plenty of protein, more than many baguettes use, in fact. But what kind, what brand? All "white" fours are not the same, not at all.

Does the flour have double zero label on it? Double zero is tailored for products that need extra extensibility, such as pizza, and sometimes croissants too (off label use). It may not be suitable for freeform loaves, especially at higher hydration level.

If you are after crumb aesthetics, it's been debunked over and over again here that 67% is perfectly fine for baguettes. Higher hydration baguettes also tend to bend as they soften, thanks to their elongated shape.

Jay

12% protein is high enough and, as Davey said, with the correct handling it'll work. 

If it is very sticky then lower the hydration. 

To further help with shaping you can also chill the dough in fridge. 

Most flours can handle 76 percent hydration if it's a yeasted dough.  Not the case with sourdough in which case maybe your starter is too acidic but we don't know that because you didn't provide much to go on :/