You will have to amend your 2020 tax return to get the unemployment compensation exclusion. But not until the IRS provides guidance.
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
