Mine is 8 just last week, so she's doing a lot more now than at 4. At 4 yo, one of the things that she liked to get involved in was anything that got her hands into the food. She wasn't using a knife yet, but anything with mixing, stirring, even some stuff at the stove (but not in the oven)
One thing we have always loved to do together is make bread. She loves to knead the bread. We still do this together frequently. Dinner rolls and pizza dough are favorites to make. We do the same with "make-your-own" pizza. Oh, we make our own sauce in the summertime from our garden and dd likes to participate in that process, too.
Making salad was another good one. She enjoyed doing the whisking when I made the dressing, tearing the lettuce, adding the other ingredients then tossing the salad.
We make a lot of homemade freezer pops. Just fruit and yogurt, blended, then frozen in molds. We rarely have juice in the house, but we sometimes do dairy-free freezer pops with juice instead.
Making hamburger patties and meatloaf and the like - again, getting the hands in the food.
Baking sweets, of course. Baking was particularly helpful with math skills because of exact measurements (as opposed to cooking, where I rarely measure anything).
I'm trying to think of things for a 4yo and not an 8yo and it's hard to remember that far back.
