You do not. Your filing status for 2020 goes by whatever it was on the last day of 2020. There is no such thing as splitting your filing status for part of the year. If you were Single at the end of 2020 and are not the custodial parent then you file as Single for 2020.
If you provided care in your home for a qualifying person, usually a child dependent, who lived in the home with you more than half the year, and if you paid more than half the cost of keeping up your household, you can still file as Head of Household. That status applies to single parents, and other single people who provide care for certain dependents, just as well as it applies to persons who are married but separated. The personal and dependent interview in Turbotax will give you the HOH status if you answer all the questions correctly and you qualify.
If you do not qualify to file as HOH, and you file as single, that status applies for the whole year. There is never partial credit for getting married, divorced, etc. in mid-year. Your tax return is always filed based on your facts and circumstances as of December 31.