«جَاءَنِي الْقَوْمُ إِلَّا زَيْدًا»
jāʾa: past verb built on fatḥ.
nūn: protective nūn before first-person yāʾ.
-ī: attached object pronoun, accusative in position.
al-qawmu: nominative subject, shown by ḍammah.
illā: exception particle.
Zaydan: accusative exception, shown by fatḥah.
This is a complete, affirmative, connected exception; hence the accusative.