Ok ... first have you filed the 2021 return yet ? and was it fully processed ? Until it is the 2021 return will not be reflected in the transcript section at the IRS.
Or are you talking about the 2020 return ?
This statement makes no sense : " I filed an extension last year after the online filing deadline."
You cannot file an extension "after" the filing deadline.
If you have successfully efiled the 2020 or 2021 return then you should have a copy of it along with the filing history ... maybe that will be enough for the underwriter :
When you e-file your federal return you will receive two emails from TurboTax. The first one will say that your return was submitted. The second email will tell you if your federal return was accepted or rejected. If you e-filed a state return, there will be a third email to tell you if the state accepted or rejected your state return.
Your return's electronic filing status history records all e-filing activity related to the return, including the Electronic Postmark. You can print it out if needed.
TurboTax Online
https://shop.turbotax.intuit.com/efile/efile_status_lookup.jsp -- enter the Social Security number of the first taxpayer on the return and the ZIP code to retrieve your filing status history.
TurboTax CD/Download software
(Windows) From the TurboTax File menu, select Electronic Filing > Show Electronic Filing Status History.
(Mac) From the TurboTax File menu, select Check E-Filing Status.
If you have been getting refunds then maybe a screenshot from the IRS showing they were paid out + a copy of the return will be enough ... the IRS now allows you to check on 2019, 2020 & 2021 here : https://www.irs.gov/refunds
