The $6k contribution for 2023 made in 2024 should be reported on the 2023 tax return. You only report 2024 contributions on the 2024 tax return.
However, for the 1099-R that you received for the backdoor transaction, you report both, as you did withdraw it to convert in 2024. Then you will indicate that you converted all of it to a Roth IRA.
Here are the full instructions to report a Backdoor Roth: How do I enter a backdoor Roth IRA conversion?
