Does the noble verse, "Do you not see that they wander bewildered in every valley, and that they say what they do not do?" mean that it is impermissible to write poetry that contains imaginary or metaphorical things that the poet did not do, like the example mentioned, even if the reader knows that they are imaginary and metaphorical?

The basic principle is that reciting poetry is permissible, and its content is what is considered, based on the hadith of Ibn Qudamah and Ibn Hajar. It is permissible to write verses that include metaphorical language and imaginative descriptions, and this is not considered among the forbidden lies. This is similar to the ruling on fictional stories. The reprehensible poetry is that which speaks falsehood, praises the most cowardly, slanders the innocent, or exaggerates in speech.