Yes, split everything 50/50. 

Thank you. So each return would show house bought for 322K, 75K improvements and 550k sale price?

That is correct.

My husband and I sold our home July 2020 and divorce was final October 2020.  Out of the proceeds from the sale, we paid off all of our mutual debt and split the rest.  How do we file our taxes with the sale of the house and how do we report the mortgage interest that we paid for 2020?

As @ColeenD3 stated above, "split everything 50/50."

Each of you can report "one-half" the sale of the house - 1/2 of the proceeds, 1/2 of the selling costs, 1/2 of the cost basis.

The same goes for the mortgage interest - each of you can enter 1/2 of the amounts reported on the Form 1098.

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