If you were still legally married on 12/31/2021 then you can only file the 2021 tax return as either Married Filing Jointly or Married Filing Separately.
Or if you are eligible you can file as Head of Household. See this for HOH status - https://ttlc.intuit.com/community/married/help/can-a-married-person-claim-head-of-household-filing-s...
