Maybe one of the Arkam Asylum related Batman games?
Trauma does something to a kid billionaire.
Anyway, just a wild guess. There's probably a small touch of that in those games.

I feel like undertale fits pretty good? How you play will determine whose characteristics you see more, either Frisk or Chara

Sally Face maybe.

Prince of Persia the Two Thrones

The Prince oscillates between himself and the demon, i forget the particularities.

Bound by Flame maybe? never played it but from what i remember you play a character possessed by a demon and are given choices whether to succumb to the demon's will or resist it

Final Fantasy VII. Any Persona game. Clock Tower 2.

引用自 DarkH：

Prince of Persia the Two Thrones

The Prince oscillates between himself and the demon, i forget the particularities.

The two original games did it first.

Cyberpunk 2077
V has . . . . identity issues.

引用自 Fake：

Cyberpunk 2077
V has . . . . identity issues.

Not sure if you can classify this as split personality.

Undertale, Needy Streamer Overload, Deltarune

Kind of the Stanley Parable but not really.

Guilty Gear titles also have a few probably Zato-One and another hybrid that i forget.

Anything else that comes to mind would be you roleplaying a character with split-personality.

引用自 Rumpelcrutchskin：

引用自 Fake：

Cyberpunk 2077
V has . . . . identity issues.

Not sure if you can classify this as split personality.

OK I should clarify myself a little (whatever 'myself" is)

1. An internal dialogue occurs between your competing personalities (arguing with each other, making commentary on your actions etc)

2. Each personility has it's own play style and goals

3. Satisfying pesonality's goals gives it more dominance (maybe there's a meter to show this)

4. The more dominant a personality, the more access you have to their skill-set (and handicaps)

5. Once a personality achieves full dominance some actions become involuntary (e.g. if you play a killer, involuntary killing my occur during difficult negotiations. If you play a negotiator then sometimes you can't pull a trigger for a cold-blooded assassination)

引用自 Sputnik：

[...] 1. An internal dialogue occurs between your competing personalities [...]

Don't know of any. Guess people better get makin'.

I was actually going to make a game that satisfies bullet points 1, 2, and 4 of yours, but not 3 or 5 - and also life circumstances have made that regrettably not possible now and in the years before now. I first came up with the concept 15 years ago. It's not really meant to be alternate personalities, but functionally that's how the concept I wanted to make works.

I reckon there's high replay value there

引用自 Sputnik：

I reckon there's high replay value there

At what I wrote? only if you're nostalgic. It's kind of a linear story despite the RPG mechanics.

Mechanically, your bullet points #3 and #5 (the two that my relevant game idea leaves out) are the two bullet points that provide the most replay value.

In mine, the protagonist and antagonist are the same character.
...so is the damsel, and several NPCs. All the same guy.
imo - Self-inserts become a lot less obnoxious when you use them for more than one character and also make them fight each other. ☯️