Make a Database of diffrent types of Items?

I am trying to make a ScriptableObject database, where I have a List. My class can be different types, but some types need additional variables. I thought of using Inheritance, but I can’t serialize that well. Now I am thinking of making different class and database for each type, but I am not sure how I can implement that. Any other way I can make my database?

So if i understood right, you want to make a generic list and save in it different type of classes? If this is the case you can just define the type of what will be saved in list as something very generic like:
List<Object> or List<T>. Then you can save all kind of classes in this list.