The works of Fyodor Mikhailovich (of course, Dostoevsky!).

Perhaps Gogol, Dostoevsky, and Tolstoy are roughly equal geniuses of Russian literature. And I could not understand why it was specifically Dostoevsky that I found so difficult to perceive.

The first reason is obvious. Nikolai Vasilyevich, in essence, wrote only one novel — "Dead Souls". The rest of his Creation consists of relatively short novellas plus "The Government Inspector".
Tolstoy, throughout his long life, wrote three novels (correct me if I'm wrong) — "War and Peace", "Anna Karenina", and "Resurrection". The rest were again novellas and short stories.
It is clear that shorter forms are read faster and perceived more easily.

Unlike them, Fyodor Mikhailovich's primary Creation lies in large novels. "The Idiot", "Crime and Punishment", "Demons", "The Adolescent", "Poor Folk", "The Brothers Karamazov", "Humiliated and Insulted", "The Gambler"...
They are all heavy social dramas; one must put themselves in the right frame of mind to read such books.

The second reason lies in the social status of the writers during their lifetimes.
Lev Nikolayevich was a descendant of two of the most noble Russian families, the Tolstoys and the Volkonskys, and moved in high circles from his youth. Hence the descriptions of balls, the dresses of beauties, etc. He knew high society perfectly. And he could afford to spend 6-7 years writing novels, unhurriedly and thoughtfully, visiting Borodino field and other settings of his novels.

Gogol came from small landowners—not noble, but well-off enough to spend a significant part of his life traveling abroad. And the heroes of his novels are precisely middle-class landowners and petty bourgeois, whose lives he knew well. There are balls and dresses too, but certainly not those of high society.

As for Dostoevsky, his fate was one long drama. From youth in the Peter and Paul Fortress, spoken for execution, standing on the scaffold. Then hard labor, forfeiture of property, service as a soldier. The unexpected death of his brother, his wife. Hence the constant feeling of guilt, the spiritual torment. The heroes of his books are precisely from the lower strata of society and are always unhappy.
And while Tolstoy could afford to write novels over many years, Dostoevsky was forced to scribble novels in a year. Undeniable talent is present, but so is a sense of being hunted and despair.

Added after 12 minutes

I kept urging him to read, but... he managed Gogol — didn't particularly like it. I tried to entice him with medieval erotic stories (the "Decameron", that is), also no luck. I even tried slipping in King — and that was a failure too. I've resigned myself)))

2 Divinora
As a man, I tell you — give him some Weller to read. "Papanin's Mauser" will break through to him.