Almost unable to finish the sentence, a huge igneous sword crushes him, while his sister yells helplessly "NO, YNGVI!".

During the impact that kills Freyr, his old sword Ingrid is ejected towards Atreus' feet, as if the Vanir god gave it to him for good as a farewell gift.

Note: Another cutscene that I find extremely ridiculous in the game is Freyr's sacrifice and escape from Asgard, and how that moment is directed: Angrboda and Fenrir's appearance as "Deus Ex Machina" from one side of the screen, Freyr parrying a huge fire sword and its effects by making propeller with his sword, a tottered Freya leaving disconsolate and fragile instead of protecting her brother as I think she would have really done, and Atreus picking up the bow opportunely forgotten to then push his father trying not to be hit by the explosion before it happens.... I find it a nonsense of a scene in general. Due to everything happens in a very convenient way to justify exactly what the developers want to happen in a forced way, in a tremendously limited space. Again creating the "theatrical feel" that I mentioned in the preface.

If there's one thing about this final battle that feels truly wasted, it's Ragnarök. A strong candidate to be a spectacular final boss as expected from a God of War. A confrontation that, in fact, would make sense to be totally out of control for not having achieved the full transformation. Instead, all he does is appear a couple of times in the background, doing his thing and barely interacting or affecting the players until the end. Exactly the same as what happens with Jörmungandr. And in the same way that I put remedy to him, I will do the same with the character that gives name to the game.

FINAL BOSS: RAGNARÖK

Before the three heroes stands a giant human-shaped mass wielding a colossal sword, around which debris from the surroundings begins to orbit, as well as elements of other realms leaked through portals to these increasingly large and numerous.

Kratos calls for calm.

–We are responsible for that thing walking on earth. If we don't want it to wipe out everything we know and to weigh on our consciences, we have only one choice: to wipe it out first.

–But... How are we going to defeat something so massive and mighty? –Atreus replies unsure.

–It's not the first time I've faced such an enemy. No matter how big they are, they all have a weakness. Stay focused to find it, Atreus. –concludes his father, trying to inspire confidence in him.

 Illustration based on the mix of some concept art from the actual game

This final boss fight against Ragnarök would have a level design in the classic hack and slash style when the developers put before the player an enemy that doesn't fit on the screen. In addition, the characters would move by jumping between the floating platforms. And sometimes they could even move by flying briefly: Kratos with Mjölnir, Atreus the same with Ingrid and Freya with her wings or transformed into a falcon. Even the control could be alternated between father and son.

During combat, as it progresses and the portals or rifts become increasingly random and unstable, the stage transports all the characters between the different realms. Passing through all of them with their peculiar environments and affecting them intermittently but chaotically.

Note: To get a rough idea of this type of bosses, there are several examples in the saga itself: as some phases of the confrontations with the Colossus of Rhodes or the Sisters of Fate in GoWII, with Cronos in GoWIII or with Aegeon the Hecatonquires in Acension. And many other examples of the style in other games, like the final boss of Devil May Cry 4 standing out especially for its similarity.
Except that in this case the combat camera, of course, would not change or open the shot and would be still close to the player.

At a certain point, (unless the player thinks of it or discovers it before) Atreus would advise to target Ragnarök's heart. Whose part of his body takes much more damage than any other. So if the player focuses a lot on attacking that region, the colossus will try to protect himself.
Until finally, once the boss's health bar is fully depleted, in the scene that follows Kratos sees it clearly.
—They... —pointing to the Blades of Chaos with his eyes —They created him, they will destroy him.
Having said this, the Spartan rushes recklessly at the giant heart while Atreus tries to stop him without success.
—No, father, it is too dangerous!

Once he manages to penetrate Ragnarök's chest, immediately he thrusts the blades imbued with primordial fire into his heart.

There is a devastating explosion that, with a blinding flash, envelops Kratos and, breaking also for the first time the one-shot camera, the screen fades to white.
During this fade, similar to the game, Laufey's voice is heard.

When the image comes back, as in the game, control shifts to Atreus who awakens in the shelter of Midgard.
At this point, both the conversations with the characters and the situation as the player advances through the stage, should convey the uncertainty of whether Kratos has died sacrificing himself.
Until he arrives at the bed where his father is lying but still alive, who wakes up little by little after several days unconscious, surprised to keep breathing.

As he dresses and settles in, Atreus briefly brings him up to date. Among other things, he show him how his old Blades of Chaos have been shattered, with many pieces missing. Kratos, while feeling melancholic, somehow feels relieved to have finally gotten rid of something that kept tying him to his dreadful past. Symbolizing perhaps the true death of the Ghost of Sparta. However, upon meeting Lúnda, she tells him that she has an idea about it and asks him to speak her later.

Subsequently, the original ending unfolds exactly as Angrboda shows them the hidden Jötnar shrine.
Atreus departs and Kratos embraces his new destiny.