Hello. I am writing this just after reading the 'Intro' chapter and here is what I can say. Keep in mind that I am pretty much new author myself, so don't take it too seriously.
1 - I think that the introduction to the world like this is a bit lazy and pretty much the same as most isekais - just a cheat code to make writing easier. Not that it's really bad but... I feel like it's better to make the world exposition in the story.
2 - Predators Ranking. I have no idea what predators are. You just said that they are are acheived by cores. What are those cores? I think you should either explain everything or just delete that part.
3 - What do you mean by "Martial arts can be found in dungeons." Like learned through some scrolls? Or when you complete the dungeon you are rewarded with martial art skill directly, like in Arifureta? (I am not sure that's how it was spelled, if you know you will know what I mean, if not then just ignore)
Now these are for the first chapter:
1 - Why the START button didn't appear when he first time used "Power On"? The only thing that changes is the encounter with the goblins, and I would get it if he got a
2 - "Stamina: 2 (every 5 points in vitality or Strength will add 0.5 point to strength)" Strenght adding to strenght? I think you meant stamina.
3 - What is the difference in Agility and Dex? Feels more or less the same to be honest, and there is no in-story explaination.
4 - I have to talk about the strange scaling of the stats and the stats overall. I guess it makes sense that the more strong you get, more vitality you get, it's natural. But it makes things complicated if you can assign stat points. I don't know how exactly it is in your story, does MC get stats through training OR some kind of level-up system gives +n amount of stat points that MC is free to assign. But in that case, your scaling of the stats (the "every 5 points in strength will add 1 point to vitality" part I mean) makes it that MC can assign all into strange, quickly becoming a glasscanon. But he won't, as he will get free vitality. Also, why Agility has no scaling like this? Another thing is that Vit feels more natural to be the averege of all stats and not Dex. But that depends on your understaning of the meaning of the stats. But again, you gave none, so all this applies to my understanding of them.
5 - Sudden game world. I had to re-read that part becouse it was just random. I mean, wasn't map showing his real surroundings? Does he has a built-in game in there?
6 - I have no idea who the MC is. I mean, how old is he? How does he look like? All I know after finishing the first chapter is that he is supposedly ugly (how much ugly, what exacly about him is ugly, did something made him ugly or he just has unlucky DNA?) and that he is a poor mercenary.
With all that said, I can't say the story is bad or anything. And I am sure that questions like that could appear while reading my own story as well.
Also, the idea with old, forgotten civilization is cool, there is not many stories with that. Or at least I haven't seen much.
Sorry if there is bad English somewhere in my feedback.
Wish you good luck.