@macuser_22
I think you lost the plot for a second.
Taxpayer here forgot their RMD for 2021, and has not filed a 2021 tax return yet.
An amended 2020 return doesn't come into it.
@Matt133
Make a withdrawal ASAP, at least as large as your 2021 RMD was supposed to be. Include a form 5329 and explanation with your 2021 tax return, that you will need to mail in. The form 5329 instructions tell you what to do.
https://www.irs.gov/pub/irs-pdf/i5329.pdf
Make another withdrawal before the end of 2022 to count as your 2022 RMD.
While some items from form 5329 carry over to the next year (such as certain excess IRA contributions) this is not a situation that will carry forward to 2022, as long as you remember to take your 2022 RMD on time.
