To everyone who helped with their advice, many thanks!
But here's the catch: after completing the game, I was amazed by yet another example of idiocy from the developers. The game itself is well-made, but the plot is saturated with Hollywood-style nonsense. The hero and heroine indulge in the joys of love on a pile of defeated enemies, and after they finish, they leave together, while the main villain emerges from the pile with a villainous smirk, and... well, let's just say, start over.

But what, do you want a 100% happy ending? If so, you can turn to Hollywood or Latin America, the creators of TV series. The universe is a constant struggle of opposites, and on the ruins of victories, a new counterbalance to the victors always begins to emerge. This is in a philosophical sense. And now, in a purely human sense - do you think that Heroes 5: Tribes of the East should be the finale of the entire Heroes series?:eek: No? Then excuse me, a hint of a sequel is an integral part of sequels.

And four races, close to the Light or something like that, after killing everyone, still end up being deceived (I just want to express myself in Russian with a curse word). Of course, such an ending justifies the add-ons and the next continuation of the game, but if in Heroes 4 it was clear that the worlds are multiple after the clash of the Ice and Armageddon blades, what strategy will the scriptwriters come up with next?

The ending justifies the add-ons - you answered your own question. And what does the multiplicity of worlds have to do with it?

I would like to hear constructive criticism, in addition to praise for Heroes 5! For example, it turns out that Railag and Agrael are the same person. Well, by the similarity of the letters, it was clear that this was an anagram. But please tell me, why the hell did he kill Nicholas in order to then save Isabel from the clutches of Kha-Beleth? Let's say he wanted to get rid of a rival, but why did he then unite the Dark Elves, kill the demons allied with them, in order to eventually rescue the Messiah of Evil, Isabel, who is pregnant?

He killed Nicholas, firstly, as a rival, and secondly, as an opponent (they were, you know, on opposite sides during the war, if you didn't notice).
The griffin's heart led Agrael to Tier, who offered him, of all things, to participate in saving the world (and, incidentally, saving Isabel). Agrael, although a demon, is a demon with a brain (he says this himself in one of the videos), so letting everything perish is not in his plans, even if he is a follower of Chaos. Plus, he has a personal interest - and so he has already "signed up" to save the world and the purification ritual...
Tier didn't come up with anything more original than to give his patient the appearance in his own image and likeness, i.e., make him an elf.
Having become an elf, Railag realizes that he can realize himself and quickly gather a large army around him, and this can be done precisely in the ranks of the Dark Elves, so he goes there.
Living with wolves means howling like a wolf - and now Railag, before our eyes, becomes a "good boy," completely rejecting the demonic principles and commandments of Chaos.
The developers presented you with an exotic picture of the inner world of a demon, his inner struggle, feelings, passions, life priorities, etc., against the background of all this, he does something today - tomorrow he may not be able to explain to you why he did it (because at that critical moment, his principles (Agrael's) change almost every hour, and you ask - why did he do this first, and then that...
And don't we always know exactly what we want when we undertake something (intuitively)?
The story of Agrael/Railag is beautiful and realistic, and you (probably, based on some templates in terms of game storylines) are criticizing it.

And in the end, it's unclear - did Zephyr save the world from another apocalypse? Did Isabel become the new Biara?

No, it was Biara who took on the appearance of Isabel.

Is there anything unclear? In the "Hammers of Fate" add-on, Isabel appears with a strangely darkened face and with an unusual bloody religion?

This is Biara, not Isabel.

What about the dedication - to Hell or Death, i.e., to Kha-Beleth or the Necromancer?

And what do the Necromancer have to do with it, and where did you see even the slightest hint of them in this case?

What about the marcol, whom Zephyr disembodied? There are more questions than answers.

And why should we "do" anything with him? He was disembodied - and that's it, and, excuse me, who cares. For a servant of Ash, this old man was too insignificant and attached to the earthly world, so I don't feel sorry for him at all.
IMHO.
In general, if the plot is really important to you, before criticizing it, read the background, play the single-player scenarios... Otherwise, it feels like you are complaining about a non-working electrical appliance, forgetting to plug it into the outlet.
No offense.