EventBusSO.cs

public abstract class EventBusBase
{
    protected readonly List<Object> _publishers = new();
    // More EventBus implementation.
    // Notably, doesn't have a member for the event, nor any methods
    // accessing the event, because it won't be possible to override
    // the event in sub-classes with different delegates. So most methods
    // have to be repeated as below.
    }
}
    
public abstract class EventBus : EventBusBase
{
    public event UnityAction OnEventRaised;
    public void Publish(Object publisher) { } // Implementation
    // ... Repeated implementation of other members accessing the event
}

public abstract class EventBus<T> : EventBusBase
{
    public event UnityAction<T> OnEventRaised;
    public void Publish(Object publisher) { } // Implementation
    // ... Repeated implementation of other members accessing the event
}

public abstract class EventBus<T0, T1> : EventBusBase
{
    public event UnityAction<T0, T1> OnEventRaised;
    public void Publish(Object publisher) { } // Implementation
    // ... Repeated implementation of other members accessing the event
}

public abstract class EventBus<T0, T1, T2> : EventBusBase
{
    public event UnityAction<T0, T1, T2> OnEventRaised;
    public void Publish(Object publisher) { } // Implementation
    // ... Repeated implementation of other members accessing the event
}

public abstract class EventBus<T0, T1, T2, T3> : EventBusBase
{
    public event UnityAction<T0, T1, T2, T3> OnEventRaised;
    public void Publish(Object publisher) { } // Implementation
    // ... Repeated implementation of other members accessing the event
}