Do I need more fermentation? Why my sourdough is flattened?
First of all, that's quite a decent looking loaf. It doesn't look dense or overly pancaked. The crumb is consistent, with good bubble formation. A lot of amateur bakers would be quite proud to achieve that result. So give yourself a pat on the back before you start trying to improve further.
Now, 82% hydration is quite high, even for a whole wheat loaf. High hydration free-form whole wheat loaves are notoriously difficult to shape well, simply because the dough is so loose. Careful shaping and skillful oven control (including steam) are necessary to get a good loft in those circumstances.
Now, three hours at room temperature is not enough time to develop significant sourdough taste. Neither is ten hours in the refrigerator. (Ten hours in a cool room would be closer.) As more fermentation occurs, however, the gluten structure will weaken, leading to a flatter loaf.
So overall, I'd suggest you try a lower hydration and a longer cold rest (but, if possible, at a slightly higher temperature than your refrigerator).