Hi Mixup
Thanks for the reply the edges are hard and the quick bread itself looks ok but when I unmold it and it starts cooling the middle sinks I'm also using a box mix to save time im thinking just going back to scratch recipes.
Also would self rise flour work better or ap appreciate all suggestions
If it's a box mix, that at least rules out leavening being the issue, they've already balanced that. That leaves oven temperature, excess liquid, or the other killer of chemically leavened baked goods: time. If you overmix the batter, or if you wait too long from mixing it to getting it in the oven, it can collapse like that. The moment you wet the baking powder in it, it starts outgassing (think Alka Seltzer hitting water). The timer has started. If you overmix it, you're beating out all the air bubbles it's creating and replacing it with just regular air bubbles. If you let it sit too long from the moment you wet it until getting it in the oven, it wears out all it's fizz and has nothing left when it gets into the heat. It relies on that sudden chemcial reaction, the "Alka Seltzer effect" if you will, to leaven the whole thing, and solidify right after.
They're called quick breads. You have to do it quickly.
Mix dry & wet, (mix, don't beat), get it in the pan, get it in the oven without any notable delay.
Cake, and by relation, scratch cookies, can be a little different. Despite also being chemically leavened, the high relative sugar content of a cake, low protein, along with a lot of fats tends to benefit from a bit of aeration, while the sugar gives it more structure and reduces the risk of collapsing from that air. Cake is only partially chemically leavened. It's also partly leavened by the emulsification of fats by substantial mixing. Quick bread doesn't get that. It's (relatively) low sugar, low fat, moderate protein, and 100% soda leavened. Box cakes, however are more like quickbreads than actual cakes.
Nobody's going to advise against going back to scratch recipies, though. It's a quick bread...you're not saving that many steps by using a box, and scratch has such better taste! The same rules apply there, though, unless, of course, your scratch quick bread recipes are fattier like a cake.
Self rise can be convenient if you're making the same muffins or biscuits all the time. Anything that saves a step and some shelf space can be convenient. But it's an extra flour to keep around where not everything you might make should have baking powder/soda in it, and you can't mix the right ratio for your particular recipe. If I were making biscuits non-stop for dinners, or muffins non-stop for breakfasts it might be convenient. Otherwise it's self-defeating since it'll often be a square peg for a round hole.