@Mike237 I can only go by what I see using the online and desktop editions to amend a 2020 tax return. That is why I post screenshots. But it does appear that many users cannot yet amend their tax returns.
TurboTax has issued this support FAQ for why you cannot amend your tax return - https://ttlc.intuit.com/community/amend-tax-return/help/why-can-t-i-amend-my-return/01/2122917
