@manisman1995
In re-reading the instructions, what the IRA custodian is instructed to do is report the entire amount in box 1 and the earnings in 2a. Then the instructions say "Enter code J and Code 8 or P". My argument here is that code P is appropriate for the 1099-R that the custodian will issue next year, since next year, code P will mean "excess earnings distributed in 2024 but taxable in 2023."
Part of the problem here is that the IRS does not actually need or want a substitute 1099-R on your 2023 return. They just want you to put the total distribution on line 4a of form 1040, and the taxable amount on line 4b. If you are over age 59-1/2, the taxable amount is zero. The requirement to create a fake 1099-R is required by Turbotax because of how Turbotax uses the forms and hidden internal worksheets to calculate the amounts to enter on line 4a and 4b. The fake 1099-R is used to make Turbotax put the numbers in the right place without having to manually edit the tax return.
If you create a substitute 1099-R in 2023, using code P will mean "earnings distributed in 2023 that were taxable in 2022" which is not the case. So I would argue that you should use code 8J and not JP. But since this is just being used to trick Turbotax into putting the numbers in the right place, it probably doesn't matter too much.
https://www.irs.gov/instructions/i1099r#en_US_2023_publink1000291991
"However, for the distribution of excess Roth IRA contributions, report the gross distribution in box 1 and only the earnings in box 2a. Enter Code J and Code 8 or P in box 7."
