This idea that you can only be a resident of one state is not a federal law (if it were, simply provide a citation), but rather a myth perpetuated by TurboTax because the software doesn't support dual state residence.
You can absolutely be a resident of two state: for example, you could be domiciled in State A, but have spent 183+ days and have a house in State B. Both states would consider you a resident.
There are many court cases to this effect: example: https://www.aprio.com/new-[product key removed]ds-double-taxation-of-dual-resident-on-investment-inc...
Here's a good article by a large tax firm: https://www.bakertilly.com/insights/[product key removed]ency-can-result-in-dual-taxation
