class C
{
    int P
    {
        get => newField;
    }
}

Generate field on newField creates it with type object (which of course results in an error):

class C
{
    private object newField;

    int P
    {
        get => newField;
    }
}

The type should be int as is correctly generated when using an expression bodied property or a block with a return statement instead.