What file did you download? Was it a .tax or .pdf or .txt file? If it downloads as a .txt file, try changing the .txt to .pdf or use a different browser to download it. It doesn't like Microsoft Edge so use something else like Chrome or Firefox.
How to get a copy after filing
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-get-a-copy-of-a-return-i-filed-thi...
