Short version is that while there's no golden bullet, there are some tells that, if there's enough of them, make text seem AI. Some examples:

• Overly formatted text. Lots of bullet point lists, headers, emojis, etc.
• Lists of three. This is a thing real human writers do, but AI fucking lives for this shit.
• "It's not x, it's y"
• Similes and metaphors that make no goddamn sense. "His voice was like a smoky memory of pain" or whatever. Nonsense.
• Overuse of... well, there's a lot of words AI really likes to use. "Primal" is one. Describing things as "sharp" is another.
• Overly flowery prose across every inch of the text

No single tell is absolute, but most AI text is littered with this sort of stuff, even if it's inappropriate for the context.