An interrogative form may not seek a literal answer at all. Its actual force follows from context.
سَوَاءٌ عَلَيْهِمْ أَأَنْذَرْتَهُمْ أَمْ لَمْ تُنْذِرْهُمْ
It is the same to them whether you warn them or do not warn them. (al-Baqarah 2:6)
The purpose is equivalence (taswiyah): the two alternatives are made equal in outcome; no choice is being requested.
هَلْ جَزَاءُ الْإِحْسَانِ إِلَّا الْإِحْسَانُ
Is the reward for excellence anything but excellence? (al-Raḥmān 55:60)
The interrogative has a negative force: the reward is nothing but excellence. The speaker is not simply requesting a yes-or-no answer but stating a principle emphatically.