Technically wouldnt the character still be the protagonist not the antagonist? The protagonist is the character you are witing for and the antagonist is their opposition. Its not the same as a hero/villain. The good guys could still be the antagonists of the person you are writing for.
No. Not even technically. The antagonist is the acting force that opposes the narrative, while the protagonist is the acting force that supports it. In almost all circumstances, the protagonist will be the point of view character. This is because it’s their story. Even in stories where the PoV changes from scene to scene, the current PoV is telling their story, this may conflict with other characters, but they will almost always be their own protagonist.
However, the antagonist can be anyone or anything, including that same character. This is why I said, it’s a very different kind of story from what the original query was interested in.
Usually, the acting forces are characters, but that’s not necessary. Personal issues such as addiction or psychological factors can easily be a story’s antagonist. Similarly, amorphous hostile forces, like, “the wild,” or “bureaucracy,” can be a story’s antagonist. You can’t really delve into an approaching winter storm’s motivations or it’s troubled childhood, but it will kill your character if they don’t find shelter and a source of warmth. It’s the antagonist (or, “an antagonistic force,” if you prefer.)
It is easy to come up with situations where the antagonist isn’t a character at all, and there numerous genres that build off that idea as standard. There also numerous sub-genres that play with the idea of the protagonist pulling double-duty as the antagonist.
Again, if your character is struggling with themselves. If they’re fighting addiction, dealing with mental illness, or just trying to find a way forward when their will has been broken, they are their own antagonist. They may not be their only antagonist, but they’re a factor. It really is possible to be your own worst enemy; when that happens in a story, that’s the antagonist.
Having someone other than the PoV as a protagonist is unusual. You can write a story where your PoV character is observing and recording the actions of another party. An example of this would be the Sherlock Holmes novels. Holmes is the protagonist, but the books and short stories are “written” by Watson.
Can you have your PoV character as the antagonist? Yeah, it’s possible, but unusual. The first example that comes to mind is A Christmas Carol, (and the endless riffs on it.) Ebeneezer Scrooge is the antagonist at the beginning of the piece. Now, the entire character arc is his transformation from miser to someone with some actual human empathy, so in the long term this might not be the perfect example. There’s also some room for discussion on self-destructive PoV characters.
One, inverted scenario, for protagonist/antagonist, would be a situation where someone was the subject of an intervention. The point of view character would be the antagonist in their own story, while their friends or family, trying to bring them back out, would be the protagonists. Though, this is a strange situation.
Ultimately, the thing about labels like protagonist and antagonist is, “they’re labels.” These are a tool used to analyze a story after the fact. It’s not something you need to worry about when you’re writing. When you are writing, worry about things like character motivation, and action. What they’re doing and why they’re doing it. Think about the opposition they’ll face, and how they will, or won’t, be able to deal with it. Asking, “who’s the antagonist?” comes after you’ve finished the work and handed it off to someone else.