If I have been separated for over a year but have not gotten legally divorced, what marital status should I file under?

Since you are still legally married your filing status is either Married Filing Jointly or Married Filing Separtely.

However, if you have a qualifying person as a dependent, you have not lived with your spouse at any time during the last six months of 2024 and you have provided over one-half the cost to maintain your household you could be eligible for Head of Household.