I'm trying to amend my 2020 tax return, but Turbotax is using my entire unemployment claim, not 10,200 max on Schedule 1, line 8.

Why are you amending?   You do not need to amend if you are only doing it because of the change in the tax law for unemployment.   The IRS is already recalculating refunds for people who filed before the tax law changed.

 

The IRS is recalculating refunds for people whose AGI is $150K or below and who filed before the tax law that changed the amount of unemployment that is taxable on a federal return became effective.   

 

 

The IRS began to send out the additional refund checks for tax withheld from unemployment in May.  The refunds are being sent out in batches—starting with the simplest returns first.   If you are eligible for the extra refund for federal tax that was withheld from your unemployment the IRS will be sending you an additional refund sometime during the next several months.  TurboTax cannot track or predict when it will be sent.  The IRS has not provided a way for you to track it, so all you can do is wait for the refund to arrive.

 

https://ttlc.intuit.com/community/tax-topics/help/how-do-i-get-the-new-unemployment-benefits-if-i-ve-already-filed-my-taxes/00/2081053

 

 

Please read this very recent news from the IRS:

 

https://www.irs.gov/newsroom/irs-to-recalculate-taxes-on-unemployment-benefits-refunds-to-start-in-may

 

https://www.irs.gov/newsroom/irs-begins-correcting-tax-returns-for-unemployment-compensation-income-exclusion-periodic-payments-to-be-made-may-through-summer

 

https://ttlc.intuit.com/community/tax-credits-and-deductions/help/am-i-eligible-for-a-new-credit-or-deduction-because-of-the-unemployment-income-exclusion/01/2211778

 

https://www.irs.gov/newsroom/2020-unemployment-compensation-exclusion-faqs

I need to submit an amended return for my 2020 AZ tax return.   AZ tax return is based off the Federal return which must be correct.  As is stands now, I can not submit an amended return for AZ.