Trouble shooting crumb

Hi, looking to get better oven spring and a more open crumb? Not sure what happened to this loaf.

Ingredients:

• 300g Bread flour

• 210 g Water

• 50g Wholewheat flour

• 70g 1:1 Starter at Peak

• 7g Salt

Steps:

1. Mix everything and leave for a hour.

2. 2x Stretch and folds + 1 Coil fold spaced by 30 minutes

3. Bulk fermented until risen by 50%. Took about 4 hours in my oven with the light on. I had to go out and it may have risen to more like 60-70%

4. Pre shape and sit for 20 minutes.

5. Final shape, into banniton and stitched.

6. Cold retard overnight

7. Baked in dutch oven @ 250 C. Cut open after it cooled down.

My suspicions:

• Overproofed?

• Dough was wet and harder to handle. I may have worked out the bubbles handling the dough?

• Still trying to figure out my oven. My breads take longer than an hour to bake a lot of the time but I thought I had it figured out following so great open crumbs recently. Those were lower hydration loaves however and I rose to 25% during bulk fermentation.

Any tips would be appreciated!