I'm having the same issue. I guess I would say it's a C++ bug.

#pragma once

#include "Base.h"

class Variable : public Base
{
public:
    Variable(const std::string& name)
    {
        _name = name;
    }
    ~Variable() {}

    std::string name() const override { return _name; }
    
    Variable& operator = (const Base& value);

private:
    std::string _name;
    const Base* _assignment = nullptr;
};

Here's what I'm doing. My first thought is overload some other operator.