Tafsir of Al-Qiyamah 75:9

[This refers to the state] where Allah—Exalted be He—will cause them both to rise from the west, according to what has been narrated from Ibn Mas’ud. This is not contradicted by the [event of] khusuf (lunar eclipse), for the intended meaning is not the technical term used by astronomers—which is the disappearance of the moon’s light due to the opposition of the two luminaries and the Earth coming between them—but rather the disappearance of its light due to a specific manifestation on that Day, or due to its conjunction with the sun, which is the muhaq (dark phase).

It has been permitted that the khusuf be understood in its technical sense, occurring in the middle of the month for example, while the "joining" occurs at its end; for there is no evidence in the majestic arrangement [of the Quranic text] indicating that their times must be identical. You know well that such a khusuf would be a disgrace to the state of the astronomers, and would scarcely cross their minds, just as the aforementioned "joining" would not.

Ibn Jarir and Ibn al-Mundhir recorded from ‘Ata ibn Yasar that he said: "They will be joined, then cast into the sea, which will become the Great Fire of Allah." The expansion of the sea or the shrinking of the two [celestial bodies] is not a matter that incapacitates Allah—Mighty and Majestic is He. The conditions of the Day of Resurrection are contrary to the natural order, and its events are metaphysical; therefore, it is not to be said: "Where is the sea in relation to the mass of the moon, let alone the mass of the sun, which is to it like a gnat compared to an elephant?" Nor should one ask, "How can they be joined and cast [there]?"

It has been said: They will be joined as two blackened, shriveled spheres, as if they were two hamstrung bulls in the Fire. From ‘Ali—may Allah honor his face—and Ibn ‘Abbas, it is said: They will be joined in the light of the Veils (al-hujub). It is also said: They will be joined and brought near, causing sweat to cover [the people] due to the intensity of the heat. Another view is that they are "joined" in the disappearance of their light; this was narrated from Mujahid and is the choice of al-Farra’ and al-Zajjaj. Thus, the "joining" is a metaphor for [their] equality in state. This has some distance [of probability], for if that were intended, the outward meaning would have been to say from the beginning: "The sun and moon were eclipsed (khusifa)."

There is no objection linguistically to attributing khusuf (eclipse) to both of them, nor kusuf. The verb did not take the feminine marker because it preceded [the subjects], and the sun is a metaphorical feminine; in such cases, both options are permissible. It appears your preference was to omit the marker in observance of the moon, which is joined [to the sun]. Al-Kisa’i said that the masculine form was used based on the meaning, the estimation being "the two lights" or "the two luminaries," but that is not particularly strong.