The taxable amount of a Roth conversion is determined on Form 8606 and is not random. Review that form to see the amounts on which the calculation is done.
If the taxable amount is varying, it seems likely that you have made a traditional IRA contribution for 2023 and your AGI falls in the phase-out range for deductibility of that contribution. When in the phase-out range, the nontaxable amount of the conversion will vary with changes in AGI as you add income and above-the-line deductions because your basis in nondeductible traditional IRA contributions is changing.
