I believe you are right, Unity cannot serialize standard dictionaries. I've used this library to serialize Dictionaries in my projects before. The README has a lot of great info features, limitations and usage. In your case, it would be:

public class GridModel : MonoBehaviour, IGridModel
{
    // This class can be defined elsewhere if desired
    [Serializable]
    public class Vec2iBoolDictionary : SerializableDictionary<Vector2Int, bool>;
    
    public Vec2iBoolDictionary grid; // This dictionary should now be serializable
    public Vector2Int dimensions;
}

Since Vec2iBoolDictionary inherits from SerializableDictionary which in turn inherits from Dictionary I don't believe you will have to change any other parts of your code that use the Dictionary. I'm not sure if there are any further steps when writing a custom editor, typically I'll just use the default editor.

Short answer is no, you can't serialize them.

But you have some options, I'll provide you with one.

Suppose you want to create a Dictionary<string, int>. You can create a class/struct that holds this information:

using System;

[Serializable]
public class StringIntPair {
    public string key;
    public int value;
}

And then, in your code, you can create a List<StringIntPair>, that will be visible on your inspector. This way you can set the values you want in the inspector.

Lastly, you can create a Dictionary<string, int> and populate it in Awake / Start method as you wish:

using System;

[Serializable]
public class YourClass : MonoBehaviour {
    
    public List<StringIntPair> exposedDictionary; 
    Dictionary<string, int> hiddenDictionary;

    void Awake(){
        foreach(StringIntPair pair in exposedDictionary)
            hiddenDictionary[pair.key] = pair.value;
    }    
}

And then you can use hiddenDictionary in the code as you wish.

The root problem here is that you don't understand why you are getting the error

name 'publisher__stats__elapsed_time_in_seconds' is not defined`.

Let's look at the code again:

Article.objects.filter(created_on__lte=datetime.now(timezone.utc) -
    timedelta(hours=0, minutes=0, seconds=publisher__stats__elapsed_time_in_seconds))

In the code above the symbol publisher__stats__elapsed_time_in_seconds is interpreted as a variable reference, which is not defined in your code. If you added

publisher__stats__elapsed_time_in_seconds = 1

just before the code snippet above, then you would not get the error. (You would also not get the results you want.) You're expecting Django's ORM to operate on the symbol publisher__stats__elapsed_time_in_seconds but before Django can get to it, the Python interpreter must interpret the code, and the way the code is written, that's just a variable name which the interpreter must resolve. Django does not get a chance to even see it.

Ok so the way to prevent the interpreter to interpret the name as a variable reference, and have Django ORM's process the name, is to use F() expressions. So you'd be tempted to just do this:

Article.objects.filter(created_on__lte=datetime.now(timezone.utc) -
    timedelta(hours=0, minutes=0, seconds=F("publisher__stats__elapsed_time_in_seconds")))

But then you'd be passing to timedelta a parameter it does not know how to handle.

As schillingt pointed out in a comment, an answer elsewhere by Lutz Prechelt shows how to move the F() expression outside the timedelta. In your case, you could do this:

Article.objects.filter(created_on__lte=datetime.now(timezone.utc) -
        timedelta(seconds=1) * F("publisher__stats__elapsed_time_in_seconds"))))