How do I download latest compatible version of an app?

So, I was trying to download PicsArt and it says that I need a 10.0 IOS version. And that's happenning to almost every awesome app and games in the App Store. And that's the problem, I almost can't download anymore because of that. Now, let's go to the question, How do I download the latest compatible version of an app that I haven't purchased before? Please answer because I'm trying to download not just PicsArt but many more...