First Loaf! First Loaf!

Hi!! Long time lurker, first time sourdough baker and poster. I thought I could judge my own bake based on what I've learned from this sub, but I'd love a bit more specific feedback from experienced bakers! One thing I already realized is I burnt tf out of the bottom – I heard putting a cookie sheet on the rack below the DO may work. Any input on the crumb would be awesome!

I followed this recipe/technique: https://grantbakes.com/good-sourdough-bread/

In brief:
-100g starter
-450g bread flour
-300h water
-10g salt

Make dough, 3x stretch and folds every hour or so, bulk ferment ~5 hours, shape, store in fridge overnight. Baked in preheated Dutch oven at 450F for 20 minutes with lid and additional 15 without lid. Waited several hours to slice.

Thank you!!