If you are legally married and living with your spouse you cannot file as Head of Household. You can only file as Married Filing Jointly or Married Filing Separately.
If you are legally married and NOT living with your spouse for the last six months of the year AND you have a qualifying child as a dependent and meet other requirements, then you are considered unmarried for tax purposes and can file as Head of Household.
See this TurboTax support FAQ for HOH when married - https://ttlc.intuit.com/community/married/help/can-a-married-person-claim-head-of-household-filing-s...
