Minimalism is about maintaining useful purpose behind the things you own and not retaining unnecessary objects. If you're a DIY person, and you have a good reason for a backyard of junk cars, that's explainable. If you buy a new iPhone every year but you don't actually use the majority of the new features (if ever at all), that's frivolity.

Minimalism isn't the ideology that (less is more)==(less things). That comes from people appropriating philosophies to compete for attention on social media, where everything is at best one-dimensional because the point is to entertain not educate. No, minimalism as a philosophy means (less is more)==(object-essentialism). You initialize solutions among what you have, and factor the time, resource, and opportunity cost into the cost-benefit of acquiring a new object. So, as I mentioned, if acquiring a backyard of junk cars is more cost-benefit savvy than having to acquire a new junk car every time you need a resource from one, it's minimalist. However, if you acquire a junk car that adds what you already have a sufficient amount of, it's frivolity.