My wife died in 2019. I filed my 2019 taxes as qualifing widower. Can I still file in 2020 as qualifying widower? How about in 2021?

If she died in 2019 you could have filed married jointly on your 2019 return. For 2020 and 2021 you can file as qualifying widower but only if you have a qualifying child living with you. Otherwise you will have to file as single. 

The qualifying widow or widower tax filing status is not available in the year of the spouse's death. 

You can generally use married filing jointly in the year your spouse passes. Then in the next two years, you can file as a qualifying widow(er) if you meet certain requirements.

To qualify as a qualifying widower, you must meet these requirements:

• You qualified for married filing jointly with your spouse for the year he or she died. (It doesn’t matter if you actually filed as married filing jointly.)
• You didn’t remarry before the close of the tax year in which your spouse died.
• You have a child, stepchild, or adopted child you claim as your dependent. This doesn’t apply to a foster child.
• You paid more than half the cost of maintaining your home. This must be the main home of your dependent child for the entire year, except for temporary absences.

@MayaD 

evidently it is available, since he filed that way.

You are a "CHAMP".  Thank you very much for your answer. I've wondered about this for some years.  vbarrio