If you were widowed in the last 2 years, and you provide care in the home for a qualifying dependent, you can use the status "qualifying widow."
If it was more than 2 years ago, and you provide care in the home for a qualifying dependent, you can file as head of household.
If you don't provide care for a qualifying dependent, there is no difference between single and widow. The choice exists in Turbotax because if you select widow, Turbotax will know to ask you about these other items. But the IRS only has single, head of household, and qualifying widow. There is no special IRS filing status for a widow without dependents.
If you are not claiming a child or other person as a dependent and you have not remarried you would file the 2021 tax return as Single. This assumes that your spouse passed away in 2020 or earlier.
And if you were widowed in 2021 (your spouse was alive for at least 1 day in 2021), then you will still file as married filing jointly for 2021.
For the year that your spouse died you can file a joint return. In the next two years after that, you can file as a qualified widow(er) if you have qualified children dependents. Otherwise, in the year after your spouse died you will file Single.