He(chaeyoon/seo) makes no sense. If he didn’t want attention, he should’ve picked a di...

i’m not sure how far you made it into the story, but the reasons behind him staying in the same field of work are pretty obvious (and if he worked somewhere else this story just wouldn’t exist) and it’s not that he simply didn’t want attention, he was just extremely depressed when he came out of the great dungeon, and the only thing keeping him alive was all the wills he was given. living as a different person from ‘seo chaeyoon’ was the only way for him to properly complete those wills, but that wouldn’t stop him from working in the same field to continue helping people. he also mentions that he would’ve immediately revealed his identity if they had just announced that their search was because of the second great dungeon earlier, so staying hidden forever wasn’t really his goal when he went into hiding

His trait as "chosen one" mean he is righteous person, he still want to protect peoples even when he keep it low profile
Plus building shield trap is also one of the will which is not absurd at all

I know, I’ve read it since the beginning. He has lots of ways to carry out his dead friends’ wishes. But I get it. it’s for the story. Even if it doesn’t make sense, it’s fine. I mean, if he wasn’t in the same field, seme and the gang wouldn’t even know he exists.

Idk what you came here expecting from MC. But MC’s main goal was not to stay hidden, (seems like this is what you think). It was to finish the will of his friends, avoid entering a dungeon, and die. That is what makes him an interesting character. He is someone so full of trama from the great dungeon, and so many of the people he has loved have died.
-Also, You say, he should have picked a different job, but have you thought, WHY he still stayed working a professional shield trap handyman? Sure, he could have worked in an office or something, but he stayed working with the shield because many guilds who create shield traps were incompetent. If you remember Rainbow guild, they create shields as well but often at a lower level than was asked for and people died because of that. And sure, MC could have ignored it but MC hates seeing people die for unnecessary reasons because of his trama. So, Of course he would keep working on shield traps, when so many others can’t even create a decent one properly.Does that make MC less competent because he still wants to help people? Like WTF?
-also what part of the story is predictable that you dislike. Like predicting that MC has trama from great dungeon, like why would you dislike that. The story does foreshadow things that are gonna happen but so what. That doesn’t take away from the actual story.

Meh

Saying it doesn't makes sense is exaggerated.
His job is literally linear with his character.
By building shield traps, he is able to protect people from dying and people underestimate shield trap maintenance workers so they wouldn’t bat an eye at the MC, which is why his hiding has been going smoothly for ten years.
Even if he hadn’t worked as a maintenance worker for the shield traps, the author probably would’ve used another approach to find him like a prophecy, an item, or tailing Taesik until he let his guard down.

Scraping the bottom of the barrel, I see.

Mehh