As of December 31, 2021, were you "legally separated under a divorce or separate maintenance decree" or did you just decide to live separately?
Do you have any dependent children? If so, where did the children live after June 24?
If you were not legally separated, with a court decree, you are still considered married for 2021. That means that you cannot file as single. You have to file as either married filing jointly or married filing separately. However, since you lived apart for the last 6 months of the year, if you have a dependent child, the parent that the child lived with for more than half the year might be able to file as head of household. TurboTax will guide you through these choices if you carefully answer the questions in the personal information section of the TurboTax interview.
There is no $10,000 limit on mortgage interest. Are you thinking of the $10,000 limit on the deduction for state and local taxes? That gets cut to $5,000 each if you file as married filing separately. Also note that if you file as married filing separately you must either both itemize deductions or both take the standard deduction.
