No, I get it. I just find that level of self-insertion to be extremely weird. I am not Jack. I enjoy Jack's story, I think he's an interesting character, I enjoy his personality. Hell, the dude liked Gojira and classic Dodge Chargers, so I'm sure he'd be fun to have a drink with at a bar. But I still know that I am not Jack, and Carol is not my adopted daughter; and that doesn't stop me from enjoying their story. Likewise, I am not Michael. I'm not dead, trapped in the afterlife, trying to sort out the personal issues of those who have died in the end of the world. I don't need to be Michael to appreciate him as a character or go along with him on his journey and enjoy the mystery of the world he now finds himself in.
So yes, I find it strange that you are unable or unwilling to keep enough mental separation, and find it necessary to inset yourself so far into an established protagonist that it causes you such discomfort.
So what if the MC is dead? That's the whole premise. I mean, have you ever played a From Software game? Dark Souls? Elden Ring? The protagonists of all of those games are some version of undead, revived and trapped in a fading purgatory of a world that is dying. I've never seen someone complain about those games on the sole basis that 'I can't get into it when my character is already dead!'. I mean, have you seen The Nightmare Before Christmas? Was the film bad because Jack Skellington was already dead? Or how about Artash Menethil, the Lich King himself, from the Warcraft series? Was Thomas Anderson's story more or less compelling when he discovered the reality of the Matrix he was trapped in, effectively dying and being reborn as Neo in a new reality? How about Malcom Crowe in The Sixth Sense? Hell, I'm pretty sure that Jesus fellow is pretty dead too.
Michael is dead, as are the people he's trying to help. That's the premise. It's not like the narrative was hiding this from you, the revelation that Michael and friends are all already dead is placed front and center; it's not an Act II plot twist. So yeah, this wasn't selling you the fantasy of self-insert romance, or an everlasting harem. This is not a dating sim, and Michael is not a blank slate protagonist. Being upset that the game's very up front premise is not what you wanted, makes as much sense as being upset that a Greek tragedy like The Iliad isn't a summer blockbuster popcorn flick like Jurassic Park.
You're not upset about Michael as a character, their personality or how they're written, you're upset cause he's dead? He's fictional. All fictional characters are dead, in that none of them were ever alive. Jack is no more alive than Michael is, so why is that such an impediment to your enjoyment? They're both fictional, both equally alive or dead, so why is Michael's journey any less interesting or compelling? Yeah, Mina has passed on, but she is no more or less ephemeral than Carol, Naomi, Alice, or Sydney. They were all well written and compelling characters, the fact that one of them just so happens to have been interacted with in the afterlife shouldn't be a mark against them. I mean, even in Now & Then, you only ever encountered characters like Missy, Ted, and Lori through flashbacks, long after they've already died within the context of the story. Does that make them less compelling characters? I would argue that it doesn't, they served a crucial and engaging role in the story; even if they were already 'dead'.
At the end of the day if you're unable to maintain a healthy level of separation between you and the fiction you ingest, you might need to take a break there champ, as you might be having trouble keeping your realities straight. But again, if this game is little more than self-insert jerk off material for you, nobody can help you with that either.