
Wait I got like a theory, there was another portal that opened inside the great dungeon when they cleared it. The portal looked like it disappeared and I feel like someone used their skill to make the portal reappear in the future where they have even greater chance of clearing it due to all the new technology or something.

OK FINALLY, so they were actually the characters, they were written into the novel, after they both died they both went into a different timelines AND world.
Ok so this is just a theory but since they both were at different timelines when they came back, while the ml was in the highschool timeline, the Huimin was in the world he believed in, and where the ml was sweet and his friend (?) until he discovered the book again and regressed into the "book" but that wasn't the book he actually read, it was the timeline where ml was already trying to change things.
Sisyphus (the title) is literally a Greek god known for being cunning and tricking ppl
He wasn't a god, he was a mortal king.
He did trick people, but he tricked gods, and not necessarily in a "manipulative" way, but more to cheat death specifically (they tried to kill him/send him to hell, he found ways to escape by
Tricking them).
He's much more famous for his repetitive futile work (pushing a rock on top of a Mountain and watching it roll off on the other side, then pushing it back again). Like, it's more what you think when you use his name in a work like this, you can also see it in the use of the word "hounds".
It COULD refer to both aspects though, we'll see.
Thankuuuuu!!!! I didn't really look properly to it, but I feel the title has alot of connection through both the ml and MC!!
It's ok ;) you weren't completley wrong