Generally, in TurboTax the best way to accomplish this is to treat each rented portion of your home as its own unit. Ex: Bedroom 1 is Unit 1, Bedroom 2 is Unit 2, and ADU is Unit 3. In this way you keep all income, assets, and expenses attributable to the unit it belongs with. No math involved.
If you haven't done that, then don't choose to have TurboTax do the math for you. Instead, you calculate the rental use % on shared items and enter that figure. Then enter the full 100% of the non shared items. It's a bit more involved, but achieves the same result.
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