How do I get verification of electronic filing of a prior year's return.?The IRS claims that I didn't file the tax return.

Once you submit your return in TurboTax Online, you'll see its status on the Tax Home screen of your account. We'll also send you emails letting you know when your e-file status changes.

You can use the IRS tool Where's My Refund to check if your e-filed return has been received.

If you don't see an e-file status for your return in TurboTax Online, you may have filed your return in a different account or using a different method.

If you used TurboTax Desktop:

1. Select File.
2. Select Check E-file status.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/electronic-filing/check-e-file-status/L9XhHDPtD_US_en_US?uid=lyd9vcrs

If you efiled, In the PDF of your TurboTax return, the last page of the federal return should be an "electronic postmark" that shows your name, Social Security number, the date and time that you e-filed the return, and the date that the IRS accepted it.