Did you read any of the resources on the Web? General resources, from investment service providers, are often easier to follow than IRS regulation text.

https://www.investopedia.com/ask/answers/158.asp

"I imagine if it's not done in time it's reportable in 2021"

It's reportable every year that it's not Removed. Including 2020.

"If the excess amount is not returned to you by April 15, you could pay taxes on the amount twice—in the year the excess occurred, and in the year it is returned to you."