The plot sounds a bit like the ending to an Outer Limits episode called "The Joining". What I get is that a new element lets the protagonist create duplicates quickly. What I don't get is why they have different memories and skills. Where do those different experiences come from?

Because of the relations and shared experiences I guess, as explained.
What the premices and starting plot remind me is the 2009 movie Moon from Duncan Jones, so much.
And in this way I think they do not "repricate", I guess the "vehicule" is full of clones. (which are already grown up, but blank pages)

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Apparently not.

https://www.pcgamer.com/frostpunk-creators-dive-into-mind-bending-sci-fi-with-the-alters-a-deep-space-game-of-survival/

a rare element called Rapidium that enables the creation of alternative versions of organic matter.

The Alters are not clones: Each one is Jan at heart, but effectively a version of him that made different choices over the course of his life. Those choices led to different outcomes: Each Alter has a unique set of skills and traits, but also different attitudes, beliefs, and personalities.

So they're version of him that made different choices over the course of a life they never lived. The explanation of what the element does fails to explain why the duplicates have memories of things that never happened.