This is a short story 12 chapters long. It's written by the author who wrote Mushoku Tensei, though it's a different style, and most certainly not isekai. Funny thing is, the author's novel was at 1st place when this work was written. (Slime tensei took the title after its anime was released)
Imagine you're trapped in a room. No reason given. You're just there, inexplicably, and you have to write your way out, surpassing even long-standing novels that have been out for a decade. You only have 1 year to do so.
It isn't easy. In fact, it seems impossible for it to be accomplished. Without cheating , that is. This is the story of a man driven insane by captivity and what it took for him to get out of the room.
I encourage you to read 'til the end, because it's worth it.