Need feedback on my sourdough - bottom burnt again

Hey everyone, I baked another sourdough today and would love your feedback! Overall, I think it turned out pretty nice, with a good rise and even an "ear," but the bottom burned again. Any ideas on how to fix this? Here's what I did: 07:30 Fed my starter 10:00 It grew 2.5x Used: 100g starter, 400g bread flour and 100g whole wheat flour, 325g water Did a series of stretch and fold a couple of times, left to ferment at room temp at 11:00 Dough rose well and had nice bubbles 6pm Shaped and put in the fridge for an hour Baked 450°F (45 min) and 400°F (30 min) The loaf looks great, but the bottom is too dark again. Could it be my not so fancy Dutch oven or oven temperature? I bake it in the center of oven which is at the same time the highest rack level. Any tips would be appreciated!