@Xtermy everything is to be reported in 2024. the retroactive payment (from 2023) will be listed separately on the bottom of form 1099-SSA when you receive it in January.
as you enter the form next year, one of the questions TT will ask if whether there is a lump-sum payment included. just watch for it and answer as appropriate. (hint: have your 2023 tax return handy as TT will as questions about that prior year return)
