If you do a Roth conversion in 2021, you'll receive a code 2 2021 From 1099-R near the end of January 2022 that you'll report on your 2021 tax return. Is you convert all of your traditional IRA(s) to Roth, which would seem to make sense in your case, all of your basis in nondeductible traditional IRA contributions made for 2020 would be applied to your 2021 Roth conversion as I described in my previous reply.
I wish that people would stop referring to a "backdoor" Roth. It's nothing more than a Roth conversion after having made a traditional IRA contribution. Roth conversions are reportable on the tax return for the year in which the Roth conversion is performed.
If you choose not to obtain a return of the traditional IRA contribution that you made for 2020, simply enter the traditional IRA contribution into 2020 TurboTax and let TurboTax automatically generate Form 8606 with the result being contribution being included on line 14 to be carried forward to line 2 of your 2021 Form 8606.
