Thank you very much John and Coleen!
Your information has already been put to use. Since I used the free online version of Turbo Tax for my 2019 and 2020 returns, I simply downloaded the IRS 1040X PDF and filled it in (using as my guide the amendments I generated on another free platform which lets you get to the final "review" stage before deciding whether to pay for a final with no watermark - why pay when I had no income in 2018-2019...). I will wait and see if Turbo Tax charges a free online user for a 2020 amendment, and if they do, I'll repeat the same exercise on the 2020 1040x on the alternative platform.
