Regarding Form 8606, you'll need to prepare 2022 Form 8606 outside of TurboTax to calculate the taxable amount if the RMD distributed from the inherited IRA in 2022, then mail it with your tax return. TurboTax does not support preparing Forms 8606 for inherited IRAs but instead asks you to just enter the taxable amount (which it stuffs into box 2a of TurboTax's 1099-R form). For the amount to include on line 6 of this Form 8606 you'll use the balance that was rolled over to your own IRA, the last balance it had before the inherited account ceased to exist.
The remaining basis shown on line 14 of this Form 8606 becomes an adjustment to your own basis on your own Form 8606 which you'll need to file when you take a distribution from what is now your traditional IRA (which would be a 2022 Form 8606 separate from the one for the distribution from the inherited IRA if you took a distribution from your own traditional IRA in 2022).
