public static ReadOnlySpan<T> GetSpan1<T>(int x)
{
    // As return statement. Works fine.

    return x switch
    {
        0 => default,
        _ => default,
    };
}

public static ReadOnlySpan<T> GetSpan2<T>(int x)
{
    // Forward declare local variable, then init. Works fine.

    ReadOnlySpan<T> span;

    span = x switch
    {
        0 => default,
        _ => default,
    };

    return span;
}

public static ReadOnlySpan<T> GetSpan3<T>(int x)
{
    // Declare and init to local variable in single statement produces compiler complaint upon return.

    ReadOnlySpan<T> span = x switch
    {
        0 => default,
        _ => default,
    };

    return span; // Compiler Complaint: "may expose referenced variables outside of their declaration scope."
}