The Maine Disaster Relief Payment is probably showing as taxable because TurboTax has not finishing updating the Maine section. The Maine Disaster Relief Program is brand new for tax year 2021.
The FAQ page says “The payment may be subject to federal income tax. To the extent the Disaster Relief Payment is taxable by the Internal Revenue Service and included in your 2021 federal adjusted gross income, you will be able to subtract the amount on your 2021 Maine individual income tax return.”
TurboTax will probably add a place for subtracting the payment when the Maine forms are finished.
TurboTax is looking to finalise the Maine forms by 20 January at the earliest. For the latest updates check out TurboTax's State forms availability table for TurboTax individual (personal) tax products.