Who is "they" who is saying you need to file a 1040X ? What mistake or missing information do you need to fix on the 2021 return? You say that you filed 2021 "by 4-15-2024"------do you mean you filed it late and mailed it in 2024? When you prepared the 2021 return did you use the CD/download software for a 2021 return? Please explain what you did.
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