Except that code provided by the payer is correct, so it's improper to file a substitute Form 1099-R (Form 4852) to change the code.
Since this distribution was originally intended to be an RMD (a requirement that was eventually waived for 2020), the distribution was paid to you. It's impermissible to use code G for such a distribution because the distribution was not paid by the IRA custodian directly to an employer plan such as a 401(k). All that was required in 2020 TurboTax was to indicate that none of the distribution was RMD (because it was no longer an RMD after RMDs were waived) and to indicate that the distribution was rolled over.
Still, the taxable result is the same whether you report the code-7 distribution as rolled over or you use code G. However, if there was tax withholding on the Form 1099-R, that causes a reporting problem because a code-G Form 1099-R cannot have any tax withholding and the presence of tax withholding forces TurboTax to include in your e-filing the details of the Form 1099-R, including the erroneously selected code G.
Now if you are instead talking about a 2021 Form 1099-R that you are entering in to 2021 TurboTax, as @RaifH said, 2021 RMDs are ineligible for rollover.
