The taxable amount of your Traditional IRA to Roth IRA conversion is being affected by the 'pro rata rule'.
When you take a distribution from a Traditional IRA (as you did when you converted the your Traditional IRA contributions to the Roth IRA) and it is reported on your tax return for the year of the distribution (2022), the year-end balance of all Traditional IRA accounts must be considered regardless of where the accounts are maintained (same broker or somewhere else).
The pro-rata rule with regard to distributions essentially means that every distribution from a Traditional IRA will be proportionally made up of pre-tax and after-tax money if the Traditional IRA account(s) is not 100% after-tax (non-deductible) money. So, if your other Traditional IRA account(s) is proportionally high on the pre-tax side, then more of the amount that was converted to the Roth will be taxed. Mathematically, the conversion amount is coming out of your total Traditional IRAs as a whole rather than the specific Traditional IRA account that may have only existed for the purpose of the back door Roth conversion.
If your only Traditional IRA account had been the one that was subsequently converted to the Roth IRA, then everything would have worked as planned, with a non-taxable event on your return.
The distribution codes on your Form 1099-R is not a factor in the calculation.
Take a look at the following discussion which may further explain the situation:
IRA Conversion to Roth & Pro-Rata Tax Obligation
@jeff B1
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