Main classes to implement ScriptableObjects variables workflow. They are not functionaly working, but will give you an overview what should be implemented. Note: there are only generic classes, and you eventually will need to create variants for each variable such as float, int, bool, Transform, Color etc.

ScriptableObjectVariables.cs

public abstract class ReadonlyVariable<TValue> : ScriptableObject
{
    public abstract TValue Value { get; }
}
 
public abstract class Variable<TValue> : ReadonlyVariable<TValue>
{
    protected TValue _runtimeValue;
    public override TValue Value 
    { 
        get => _runtimeValue; 
        set => _runtimeValue; 
    }

    void Awake()
    {
        _runtimeValue = Value;
    }

    protected abstract TValue InitialValue{ get; }
}

public abstract class ReadonlyVariableReference<TValue, TVariable> : ReadonlyVariable<TValue> where TVariable : ReadonlyVariable<TValue>
{
    [SerializeField] protected TVariable _variable;
    public override TValue Value { get => _variable.Value; }
    public virtual TVariable Variable { get => _variable; }
}

public abstract class VariableReference<TValue, TVariable> : ReadonlyVariableReference<TValue, TVariable> where TVariable : Variable<TValue>
{
    public override TValue Value { get => base.Value; set => _variable.Value = value; }
    public override TVariable Variable { get => base.Variable; set => _variable = value; }
}

public class SerializedVariable<TVariable, TValue> where TVariable : Variable<TValue>
{
    [SerializeField] private TValue _plainValue;
    [SerializeField] private TVariable _variable;

    public TValue Value
    {
        get
        {
            // if variable reference is set in the inspector, then use value from it
            if (_variable != null)
                return _variable.Value;
            // otherwise, use a plain value, that set from inspector
            return _plainValue;
        }
        set
        {
            // the same logic for setter
            if (_variable != null)
                _variable.Value = value;
            _plainValue = value;
        }
    }
}