You can not file as single if you were legally married on December 31, 2020.
As a married person, you could file as head of household if you provide the main home for a qualifying child and your spouse did not live with you for the last six months of 2020. The qualifying child would have to be your dependent.
While you could file as Married Filing Separately, there are usually tax advantages to filing jointly. If you file separately, see what your total refund or amount owed comes to. Then see if it is more beneficial to file jointly. You can use either Married Filing Separately or Married Filing Jointly.
If you spouse's only income is social security, then they will not need to file a tax return if you file as Married Filing Separately or if you qualify to file as Head of Household.
