Thanks for this useful explanation (as always). I would only correct you on the verb "s'agir" (a tricky one) which wouldn't be used in this case (de quoi parle le film ?).
handla om = be about
handling = plot
The verb "handla" on the other hand means "act" or "shop".
present continuous here in english is not correct when its like "what is the film dealing with"? or is it not because a film does it in general and not the time we talk about it?
It's correct in terms of grammar, but when it comes to permanent properties (a film can be about one or many things, and it can't suddenly stop being about that thing or things) you should use the simple present tense.