A 2020 tax return can be amended for a tax refund at any time on or before May 17, 2024 or if a 2020 extension was filed then the latest date to file is October 15, 2024.
It taxes are owed on the 2020 amended return it can be filed at any time and does not have a cutoff date.
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
