In Judgment Day, Marvel fully clarifies the Eternals' fight with the X-Men, since their immortality is revealed to be excessive deviation.
The Free Comic Book Day 2022: Avengers/X-Men special clarifies the Eternals' imminent conflict with the X-Men, detailing the big mutant retcon in greater detail, as the path to Judgement Day heats up at Marvel Comics. For months, it appeared that Judgement Day would alter the mutant race's past, making them descended from Deviants rather than humans, but now it appears that the Eternals' freshly constructed Resurrection Protocols will pit them against the X-Men.
The Resurrection Protocols are a method by which The Five, a group of five mutants respected in Krakoan society who employ a "circuit" of their abilities, can resurrect any dead mutant into a newly cloned body, with their complete consciousness and essence implanted in the husk via Cerebro. Since the release of House of X/Powers of X in 2019, mutants have had access to this technology. Despite Cyclops' threats to reveal this enormous secret, the X-Men and Quiet Council have managed to keep their immortality hidden from the rest of the world... up to now
In Stunning Judgment Day Art, The Avengers And X-Men Take On A Celestial
The story "Of Deviation and Mutation," written by Kieron Gillen with art by Dustin Weaver and Marte Garcia, begins millions of years ago, with Uranos, the former leader of the Eternals, contemplating the slaughter of a group of "thinky monkeys" who have mutated and developed a hive mind, while Odin of the BC Avengers looks on. Uranos argues that the monkeys' mutation could lead to the destruction of the world, and as their Celestial goal is to eliminate any creature that exhibits "extreme deviation," he resolves to wipe out the mutant colony to save the globe. In the current day, the Avengers are battling a giant monster when the heroic Eternals step in and easily defeat it, with Sersi explaining that fighting the creature was not an option and that, "When something deviates too much, we have to step in." Before explaining the longevity of mutants and disclosing that Jack of Knives, one of the four Eternal crime bosses, had successfully invaded Krakoa and observed Cyclops' resurrection after death, the Earth machine ponders the nature of mutation and deviation.
When the retcon about mutants being "Deviants" was first announced, it sounded like the entire history of mutantkind would be retconned, but it now appears that the Eternals will view mutant immortality as a "excessive deviation," similar to how the "thinky monkeys" developing hive-mind was a mutation that Uranos considered deviant. The Eternals, like the mutants, are eternal, and their rebirth process is similar to the mutants', therefore it appears that the Eternals have an inflated sense of self after millennia of existence. Druig, the Eternals' ruler Thanos' right-hand man, has been working with Moira MacTaggert to incite war between the Avengers, X-Men, and Eternals, and Jack of Knives relays this information to him.
With Thanos in control of how and when Eternals are resurrected, there's a chance he'll be able to change the literal internal coding within their minds, causing them to be unable to stop themselves from attacking people with the X-Gene, which is why the previews for Judgment Day show heroic Eternals like Ikaris and Sersi attacking the X-Men, something they'd never do normally.
"Mutants have conquered death - Now the Eternals must conquer the mutants!" says the back cover of FCBD 2022: Avengers/X-Men #1, which is an ad for the impending Eve of Judgment Day one-shot. And it's evident that Druig, Thanos, and Moira intend to do just that.