Do you have a qualifying dependent? You cannot file HOH unless you have a qualifying dependent.
Am I Head of Household?
https://ttlc.intuit.com/questions/1894553-do-i-qualify-for-head-of-household
https://ttlc.intuit.com/questions/2900097-what-is-a-qualifying-person-for-head-of-household
If you qualify as Head of Household, when you enter your marital status (single or married filing separately) into MyInfo, and then enter your qualifying dependent, TurboTax will offer HOH as your filing status.
Are you eligible for Head of Household? Do you have a qualified person as a dependent on your tax return? Do you provide over one-half the cost to maintain the home?
See this TurboTax support FAQ for HOH - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-filing-status/qualify-head-household-2021/L0NxUtVc2_US_en_US?uid=m5x19jkx