this is a trope that really annoys me. if your main character is the actual author of the world he gets sent to, why on God's green earth wouldn't he know everything about it? i would give it a pass if it was the author's assistant who gets isekai'd. that way, the MC would be close enough to know most things but would not have access to the authors own mind, which would explain him not knowing certain aspects about the story.
by all intents and purposes, the MC of this story is God. he might not have actual godlike power to freely manipulate and alter the story whenever and however he wants but what he should have is the knowledge of anything and everything in the world. the MC not having even that is concerning. this begs the question, does the author even know what he wrote? or is the story he created so shallow and barebones that whatever otherworldly force transported him just filled in the gaps so that the world will have substance. each option does not bode well for the MC as a writer.
just imagine how insane it would be if Kishimoto got transported in the Naruto world and he doesn't understand how Jutsus work. like what?
regardless of what type of story and setting it is, if you're a writer, there will have to come a point where you will imagine yourself being in that world. you know exactly how it operates and how to take advantage of it.
in this manhwa the MC is literally using a piece of magical paper with the consciousness of a character he made to get information... bro... you wrote the damn thing. if anything, the paper should be asking YOU what is going on. not the other way around.
and this concept brings up an even bigger problem... how did that character lose in the story? because from what i could see, he had the power to actually summon (from his perspective) God, the author himself, against his will. a fictional character actually tore through the 4th wall and yoinked his creator. do you understand how insane that is? this is a super meta and interesting concept. a shame it's executed poorly.
example, in chapters 15-16 there is a room full of artifacts and weapons. why doesn't he know every single item displayed? not just that, there's this one item, a necklace that seemingly is so valuable, the magic paper said to "offer a god" just to get information. who knows what "offer a god" means but that seems like an immense requirement for information. clearly it is a super important item. and why does the MC know nothing about it?