since you were still married on 12/31/19 your only choices are married filing joint or married filing separate (MFS). generally in your situation a joint return is best. if you file MFS certain credits will not be available. - earned income credit, child and dependent care credit. certain other deductions and credits will be lost - education credits, student loan interest, phaseout of IRA deduction.
the fact that you weren't married until 2019, doesn't affect you ability to file a joint return
