I was in the same situation as you a year ago and as someone who is about to do maths at uni, there is absolutely no need to make your irp related to that since it's probably not something worth writing about in your personal statement. I would say it's best to go with something you're genuinely interested in and that is debateable (of course if that topic turns out to be mathsy then all the better but don't actively make it that JUST to make it relevant to your degree). One other piece of advice is whatever you choose, don't make it something that's very current or you'll end up constantly having to change your irp to keep it up to date.
Something to do with the french economy
You could explore how good the French education system is.
If you like reading/films/shows then you could review a french book/movie/show that you aren't going to study in school of course ( in hindsight I feel like this was what I should have done for my irp since I'm a book nerd)
France is famous for their nuclear energy sector and there's always some sort of debate going on about it if you're interested in that