I requested a RMD withdrawal in Dec 2023 , but it was posted on Jan 4 2024. Can I add the transition to my 2023 taxes or do I need to wait until 2024. The bank told me I had to fill out another tax form but I don't have a 2023 1099-R to enter.

[fanfare]

You  have a 2024 distribution.

You have to give your custodian enough time to get the money withdrawn by Dec 31,

[SteamTrain]

i.e., live and learn. Never wait until the last minute to take an RMD.

If it was your first required RMD...i.e. you turned 73 in 2023, then it's  OK to have it taken in 2024, but you will have to take your actual 2024 RMD before the end of 2024, and will have two RMDs adding to your AGI for 2024.

[dmertz]

2023 was not the first year that you were required to take an RMD you must complete Form 5329 Part IX requesting a waiver of the excess accumulation penalty now that the RMD has been completed, albeit late.