Do not try and amend the 2020 tax return for the unemployment compensation exclusion until the IRS has had time to make the changes to the tax code.
After the legislation has passed Congress and after the President has signed the legislation and after the IRS has written the rules, regulations and procedures. And after the IRS has changed any forms or schedules to accept the tax code changes. And after the IRS has approved the changes in the TurboTax program that apply to the tax code changes, then it will be available for the users of the tax preparation software.
This can take anywhere from several weeks to several months before it becomes available.
See this TurboTax support FAQ for information on the American Rescue Plan - https://ttlc.intuit.com/community/tax-topics/help/how-will-the-stimulus-package-impact-me/00/1393859
