I'm slightly confused by your explanation of the timeline, but the general rule is that:
If you convert a traditional IRA to a Roth IRA, and you have a non-deductible basis in the traditional IRA, that part of the conversion is not taxed, but any other growth is taxed (since it was previously growing tax-free).
For example, if you contributed the maximum in 2020, 2021 and 2022, your non-deductible basis in the traditional IRA is $18,000. This should be shown on your most recent form 8606. If the value of the IRA is $30,000 on the day you convert it to a Roth IRA (and you convert it all), $12,000 will be taxable income.
