VolvoGirl's reply is correct.
Code B has nothing to do with a Roth IRA. Code B applies to distributions from designated Roth account in a qualified retirement plan like a 401(k), not to distributions from a traditional IRA (or any other type of traditional retirement account).
The message TurboTax is giving you regarding $6,000 is the result of an entry you made under Deductions & Credits -> Retirement and Investments -> Traditional and Roth IRA Contributions. Nothing about a Roth conversion is to be entered there. The Roth conversion is entered only by the entry of the code-7 Form 1099-R that is reporting the distribution from the traditional IRA. It seems that you inappropriately entered the $10,000 as a regular Roth IRA contribution, so you must correct that entry.
Since RMDs were waived for 2020, none of your distribution was RMD, even if the original intent of the distribution was to be an RMD.
If you've already entered the Form 1099-R, delete it. When (re)entering the code-7 Form 1099-R, indicate that none of it was RMD, indicate that you moved the money to another retirement account, indicate that you did a combination of rolling over, converting and cashing out, then indicate the amount ($10,000) that you converted to Roth.
The link or button to add another Form 1099-R is beneath the list of the other Forms 1099-R that you have already entered.
