Rust borrow checker rejects self-referential struct even with Pin and PhantomPinned

I'm trying to create a self-referential struct in Rust where one field holds a reference to another field. Even using Pin> and PhantomPinned, the borrow checker still complains.

struct SelfRef {
    data: String,
    ptr: *const String, // raw pointer to data
    _pin: PhantomPinned,
}

After constructing and pinning, I set ptr to point to data. But when I try to access through ptr in a method that takes &self, the compiler says the lifetime is wrong. Is there a safe pattern for this without unsafe? Or is ouroboros/self_cell the only practical approach?