Since you apparently still had some funds in a traditional IRA at the end of 2021, only some of your basis in nondeductible traditional IRA contributions will be applied to the Roth conversion with the remainder of the basis to be applied to subsequent distributions from your traditional IRAs. If the amount rolled over from the 401(k) to your traditional IRAs was greater than $17,500 and all pre-tax, more than half of your 2021 Roth conversion will be taxable.
I am not sure how to account for this when I do taxes this year.
