Registered domestic partners (RDPs) who file single for federal must file married/RDP filing jointly or married/RDP filing separately for California.
If you are an RDP and file head of household for federal purposes, you may file head of household for California purposes only if you meet the requirements to be considered unmarried or considered not in a domestic partnership.
If you filed a joint tax return and either you or your spouse/RDP was a nonresident for 2021, you must file the Form 540NR, California Nonresident or Part-Year Resident Income Tax Return.