How can I get a copy of my original 2021 1040 tax return? It's only showing me the amended copy that I haven't filed yet.

If you did not save a PDF of the 2021 original tax return before starting to amend the return, the original Form 1040 is gone.

Go to this IRS website for free federal tax return transcripts - https://www.irs.gov/individuals/get-transcript

For a fee of $43 you can get a complete federal tax return from the IRS by completing Form 4506 - http://www.irs.gov/pub/irs-pdf/f4506.pdf