I always find it amusingly parochial in time and place, when people assume everyone everywhere has alwats been terrified and horrified by death.
Consider Día de Muertos, a legacy of Nahuatl attitudes to death (a group that included Aztecs. Also the Brazillian Candomble worship of Boa Morte, Our Lady of Good Death, which involves recognising the relativity of death and is rooted in African religious traditions. I would relate Aztec human sacrifice, & pre-European Subsaharan African slave trade, to far less predictable weather cycles (eg El Nino/La Nina) than other regions, and so widely varying ecological carrying capacity of humans. That made for cultural pressure to accept sacrifice and slavery as part of a cycle, as the Canaanite Moloch seems to have had human child sacrifice to by parents who couldn't afford taxes, and debt and conquest slavery by the Hebrews (many wars are driven by existial threats to a community, so conquest can often be linked in the Ancient World to reduced ecological carrying capacity, just like sacrifices in response to bad harvests).
Kali, as a necessary part of the cycle, keeping other forces in check including slaying demons, and granting moksha, spiritual awakening.
The Daoist Taiji, with yin as necessary, to make space for creation and becoming (although also the founding Qin emperor's life-shortening pursuit of immortality).
In Greek mythology, consider the Aeneid, and the metaphor of entering the land of the dead by offering a golden bough - arguably by taking a place in the lineage of making art that transcends time (see Yeats last verse of Sailing To Byzantium). Also consider what we know of the theology of the Eleusinian Mysteries, which both Plato and Aristotle undertook, and seem to have been about recognising our place in natural cycles, in relation to Olympian Demeter and Cthonic Persephone, in relation to the harvest.
Until modern times most religions have focused on cyclical aspects of cosmology. Many look towards being reborn. And I describe religion in general as preoccupied with symbolic immortality, in this answer: What are some philosophical works that explore constructing meaning in life from an agnostic or atheist view?
Buddhist philosophy seeks the Middle Path, between an eternal soul, and everything we are finishing with our physical death. The focus of modern culture on individualism and self-gratification puts our culture on the latter end of that spectrum with a picture of our concerns finishing at death; Christianity especially as influenced by Boethius and his Stoic ideas, focuses on the afterlife above improving the world. Our actions do have repercussions after our deaths, we inherit things and ideas, and we have stewardship, and we pass things forward. Recognising that, is key to making peace with death.
Freud posited the Death Drive, which subsequently has been associated with Thanatos, as the converse drive to Eros. I would identify Nietzsche as grappling with the Death Drive in his discussion of 'overgoers', and with the role of symbolic immortality with his picture of the Ubermensch. You may like this answer on these: Trying to Understand Quote by Nietzsche
Biologically, immortality is a massive obstacle to evolution, and very few animals have such bio-indefinite mortality, indicating the lack of net advantage. It should be compared to apoptosis, as a mechanism to manage tumour formation. From the perspective of Multi Level Selection, death is absolutely not a bug, at species level.
We all must die, so getting reconciled with that is necessary even for the biologically immortal (brain transfer/recording involves becoming a new kind of being, I'd argue, and even then finite). In Buddhist philosophy this is linked to accepting The Three Marks of Existence as inescapable, especially impermanence. Only then can we awake, to the true nature of things.