If your spouse passed away in 2020 you can file as Married Filing Jointly on your 2020 tax return.
how do I keep from getting an overpayment on stimulus benefits if my spouse died before the 2nd stimulus came out?
You are eligible for both you and your spouse's stimulus payments if your spouse was alive for any part of 2020.
The IRS says: “A payment won’t be issued to someone who has died before January 1, 2020. If you filed a joint return in 2019 and your spouse died before January 1, 2020, you won’t receive a $600 payment for your deceased spouse, but you’ll still be issued up to $600 for you and $600 for any qualifying children, if all other eligibility criteria are met.
Regarding eligible individuals who died in 2020, the Recovery Rebate Credit may be claimed on line 30 of their 2020 tax return.”
Refer to Will a deceased individual receive the payment? (added January 5, 2021)
If you only got one $600 payment, then you are entitled to claim the second payment as a Recovery Rebate Credit on your income tax return. Page 57 of the Form 1040 instructions say:
Generally, you are eligible to claim the recovery rebate credit if in 2020 you were a U.S. citizen or U.S. resident alien, weren't a dependent of another taxpayer, and have a valid social security number. This includes someone who died in 2020, if you are preparing a return for that person.
Thank you for your help! I wonder if it matters that we didnt file a joint return last year. I actually dont know if he filed at all since we were living apart at the time.