martial status

You have not mentioned whether you have children.   If there are children then the parent who has the children for at least 183 nights of the tax year can file as Head of Household instead of filing as married filing separately.  That is when it is important to distinguish whether you lived apart for at least six months because another condition to filing HOH is that you must have lived apart for at least the last six months of 2021.

If there are no children  or qualified dependents involved then it is moot and your answer as to living apart will not affect your tax return.

If you were legally married at the end of 2021 your filing choices are married filing jointly or married filing separately.

Married Filing Jointly is usually better, even if one spouse had little or no income. When you file a joint return, you and your spouse will get the married filing jointly standard deduction of $25,100 (+$1350 for each spouse 65 or older)  You are eligible for more credits including education credits, earned income credit, child and dependent care credit, and a larger income limit to receive the child tax credit. 

If you choose to file married filing separately, both spouses have to file the same way—either you both itemize or you both use standard deduction. Your tax rate will be higher than on a joint return. Some of the special rules for filing separately include: you cannot get earned income credit, education credits, adoption credits, or deductions for student loan interest. A higher percent of your Social Security benefits may be taxable. Your limit for SALT (state and local taxes and sales tax) will be only $5000 per spouse. In many cases you will not be able to take the child and dependent care credit. The amount you can contribute to a retirement account will be affected. If you live in a community property state, you will be required to provide additional information regarding your spouse’s income. ( Community property states:  AZ, CA, ID, LA, NV, NM, TX, WA, WI)

 If  you are using online TurboTax to prepare your returns, you will need to prepare two separate returns and pay twice.

https://ttlc.intuit.com/questions/1894449-married-filing-jointly-vs-married-filing-separately

https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states

https://ttlc.intuit.com/questions/1894449-is-it-better-for-a-married-couple-to-file-jointly-or-separately

It doesn't matter. If you are married, you have the option to file jointly if both parties concur or separately. It is your choice.

If you have not lived together the last six months of the year and you otherwise qualify, you can be Head of Household.

Head of Household

You may be able to file as head of household if you meet all the following requirements.

1. You are unmarried or considered unmarried on the last day of the year. See Marital Status , earlier, and Considered Unmarried , later.
2. You paid more than half the cost of keeping up a home for the year.
3. A qualifying person lived with you in the home for more than half the year (except for temporary absences, such as school). However, if the qualifying person is your dependent parent, he or she doesn't have to live with you. See Special rule for parent , later, under Qualifying Person.

Qualifying Person

See Table 4 to see who is a qualifying person. Any person not described in Table 4 isn't a qualifying person.