Gemini says that “Il s’agit de ma propriété personnelle” would be used in a legal or explanatory context where you are defining a situation.
Instead it suggests:
“C’est ma propriété personnelle.” (This is my personal property.) - Use this if you are being searched by security, or if you are asserting a formal boundary.
“C’est à moi.” (That belongs to me / It’s mine.) - If someone picks up your phone or touches your car. This is the direct equivalent of “That’s mine.”
Possibly, but the French sentence just sounds weird to me.
When I read the English sentence, it feels natural: You want to emphasize the fact that something belongs to you, maybe you want to assert a formal boundary, as Gemini says. I feel like it works quite well, whatever that thing is.
When I read the French sentence, it doesn’t really “work” i.e. I feel like we wouldn’t say that to convey the “This stuff is mine!” idea.
Gemini says in a legal context, but even then…
Maybe if you’re talking to a notary/solicitor/attorney and want to make it clear to them that you are the sole legal owner of a house/piece of land.
What Gemini suggests is “interesting”, because really the only thing Gemini changes here is the verb: “c’est” vs. “il s’agit de”.
If you consider that “il s’agit de” is a fancy way of saying “c’est” (which in this case, it pretty much is), then the core meaning remains the same, and so what I said above still applies.
Indeed, this is very common way of saying that something belongs to you.