فُتِحَتِ الْأَبْوَابُ — The doors were opened.
فُتِحَتْ: past passive with feminine tāʾ; before the following alif-lām, a helping kasra appears in connected pronunciation.
الْأَبْوَابُ: broken plural of a nonhuman noun, nominative passive subject with ḍamma.
A singular feminine verb is common with nonhuman plural nouns. The visible plural noun does not make the preceding verb plural.