You have to take each piece separately.  So if there was a $6K contribution timely designated for 2022, you file an 8606 in 2022 (and presumably that calculates that it was non-deductible and establishes $6K basis for TY2022).  Then your 8606 in 2023 will show a $6K starting basis and another $6.5K non-deductible contribution.  Then you have a mid-year $12.5K conversion and report the 12/31/23 FMV as $0.

Keep in mind, this blows up if there are any other Traditional IRAs (including rollover IRAs, SEP-IRAs, and SIMPLE-IRAs) because they will have FMV on 12/31 with no basis.  Everything gets aggregated for tax/8606 purposes.

Rick