Your husband's 2023 RMD was required by law to be paid out of the 401(k) before (or coincident with) the remainder was rolled over to your account. If your husband's plan failed to do that, the code 4G Form 1099-R is incorrect in that it includes an amount ineligible for rollover and your account contains an excess contribution. Correct handling would have resulted in two Forms 1099-R from your husband's plan, one reporting the distribution of the 2023 RMD (code 7 if paid to your husband before his death, code 4 if paid to you as beneficiary) and the Form 1099-R with code 4G for only the portion eligible for rollover.
