How to eFile amended returns? Amending Form 8606 for 2021, 2022, and 2023

I need to file amended returns for the last 3 years due to not handling nondeductible IRA basis tracking correctly on form 8606.  Per the IRS, you can use tax software to electronically file your 1040-X. File an amended return | Internal Revenue Service

I used TurboTax Deluxe and e-File'd for each year's original return. As an example, for TurboTax 2021 I go through the steps and says that 'e-Filing is Closed for the season, You can file by mail' the tax season closed 10/17/2022.  However, I get to the end there is an option to "Transmit Returns Now", when I click the button, I get a 'Correct your Signature date' which is signed with today's date of 3/30/2025.  Then TurboTax indicates the signature date must be between 1/1/2022 and 12/312022. 

 

How to efile:

Question 1: Will TurboTax handle it once you are past the end of the year it was originally due?

Question 2: How can I electronically file (eFile) my amended tax returns for previous years (2021, 2022, 2023) through TurboTax? 

 

If I have to print and snail mail, I have a couple more questions:

Question 3: If the only change is form 8606 for nondeductible IRAs and there is no change to anything else with 0 payment/refund due on the 1040-X, what do I need to print to send?  I have read either a) the whole return or b) just the 1040-X and Form 8606 or c) is there something else? 

Question 4: Can I mail all 3 amended returns together in one envelope or must they be separate?

 

Question 5: With 2024 taxes due in two weeks, should I file an extension for 2024 to allow the amended taxes time to process first or can I submit it now using the corrected tax basis numbers?

 

Thanks in advance for your help.