Per IRS Publication 17 Your Federal Income Tax (For Individuals), Chapter 3, on page 25:
If your spouse died in 2020, you can use married filing jointly as your filing status for 2020 if you otherwise qualify to use that status. The year of death is the last year for which you can file jointly with your deceased spouse. See Married Filing Jointly, earlier.
You may be eligible to use qualifying widow(er) as your filing status for 2 years following the year your spouse died. For example, if your spouse died in 2019, and you haven't remarried, you may be able to use this filing status for 2020 and 2021.
This filing status entitles you to use joint return tax rates and the highest standard deduction amount (if you don’t itemize deductions). It doesn't entitle you to file a joint return.
Eligibility rules. You are eligible to file your 2020 return as a qualifying widow(er) if you meet all of the following tests.
After the two years, you may be able to file as Head of Household, if you qualify.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.