Updated 2021-06-22: look at this topic.
Defold is too heavy for playable ad (in my opinion). PixiJS and any other lightweight JS engine are much better for this.
But I made the project as a demonstration that Defold can fit into one HTML file that less than 2mb.
Now you just need to do a playable ad and submit it to Facebook for approval
If you succeed, I’ll make a complete asset out of this project.