Oh gee, give me a second please

Exactly ¯_(ツ)_/¯ who cares if he is raising the dead, if he saves the living?

Baek doesn't want the healer, who's been his long time friend, to be a part of the shadow army. It's explained properly in the novel.

I have a question. Can't really find the novel chapter but did Jinwoo stop to explain what he was gonna do there? Cause here in the manhwa he doesn't so we can't really read this as Baek not wanting healerboy to be "part of the shadow army": if Baek clearly states that in the novel that would be either a perfect guess of what's gonna happen or just the writing going meta. Also here in the manhwa it's shown that he understands Jinwoo's power only after seeing the result, bringing us to think that during the first two fails when he was asking "what are you doing?" he really didn't know what was happening.

So (at least for the manhwa) my conclusion still stands:
He's being the annoying sibling that asks you to do things and then butts in with a "whatcha doin? :3" and you're like maaan just give me a second and let me work.

I'll try to find this scene from the novel for you. It's easier that way. If I can't find it, I'll attempt to explain.

I found the scene...if you want then you can read the full chapter here,
https://www.readlightnovel.org/solo-leveling/chapter-122

Firstly, I'm sure you already know that the entire novel cannot be made into the manhwa, therefore many, many explanations are left out. Only important scenes are kept. Which may cause wildly different perceptions of the scenes when reading the manhwa (without all background info).
So after chopping up a lot of dialogue and explanation, in the manhwa it looks like Baek immediately stops Jinwoo. That's not the case in the novel.

Secondly, even before reading chapter 122 you have understand the background of the Healer (i don't remember if this was explained in manhwa, sorry).
The Healer was with Baek when they went to the island expedition last time. They lost an important person in that raid. Hence, the healer didn't want to join this raid. But because of Baek, he joined. So in conclusion the Healer wants / wanted to stay out of all the fighting.

Thirdly, about Jinwoo.
In the novel, he doesn't indiscriminately make every powerful person he killed a part of his army. He has some respect for the dead, so to speak. So, he's against making The Healer come back. But he only does so to save her life.