There are various eras one can transmigrate into from the Naruto universe. First is when the sage of six paths was around with indra and asura
Then there is the Warring States period, the era of the 3rd hokages generation, the sannin generation, minatos generation, all the up to Naruto's generation. Along with many possible AUs for the universe.
Nobody does Borutos generation.
But imaging a Transmigrator who came to an AU Naruto Verse where the Moons eye plan succeeded. Where Madara, Obito, or Kaguya truly trapped the world in an eternal illusion.
The Transmigrator realizes that they are in the infinite tsukiyomi either through meta Naruto knowledge or the manifestation of their "golden finger."
As for what this golden finger is? It has to be something that will bypass the illusion, provide, escape, and the eventual destruction of the infinite tsukiyomi.
Let's say that the Transmigrator had the Infinite Void template from the previous chapter. They would slowly accumulate data from the tsukiyomi itself, hijack their own illusion and transform it into a void(a conceptual space, a void is neither matter nor illusion but a manifestation of the conceptual infections sphere of influence that void be both or neither). They could gradually infect the dreams of others within the infinite tsukiyomi transforming their dreams into voids. Corrupting the infinite Tsukiyomi and in turn gaining power over all of humanity and the world.
Or they could have other kinds of abilities that could transform the illusory into reality like the Cursed Technique Comedian.
Any ability or system that could break you and others free.
But there would be challenges. Let's say you could first act through the world tree and everyone in it. But then you would need to leave to reach those beyond one at a time.
At that point you would have to evade or fight the caster of infinite tsukiyomi, deal with the humans left out to ensure long term human survival. Consul those separated from their illusionary worlds like recovering drug addicts.