How is the theme of exile represented in "Dedication" by Czleaw Milosz and what are the symbols in the poem?

With “Dedication,” Czesław Miłosz proposes the poem as an offering to those who perished in the siege of Warsaw as well as those forced to succumb to the German control that was then imposed. Exile is both a physical condition of leaving the city and an existential state of moving away from that control. The speaker calls attention to the errors in saying goodbye to a place and to the past: “You mixed up farewell to an epoch with the beginning of a new one.” While the dead are literally gone, the speaker indicates that they have been haunting him, which he aims to stop by leaving behind the words of his poem:

I put this book here for you, who once livedSo that you should visit us no more.

The symbolism used includes clouds or fog for hidden or obscured truths: “silence like a cloud” and “white fog.” The speaker also uses birds and their cries to symbolize the dead and their lost words: “the wind throws the screams of gulls on your grave” and “the dead who would come disguised as birds.”
https://www.poetryfoundation.org/poems/49458/dedication-56d22b9082a83