If you want to unzip natively on iOS you can make a Shortcut to do it. It takes about five minutes with Apples free Shortcuts app.
Once downloaded from the App Store, you create a new Shortcut, drag in the ‘Extract Archive’ and ‘Save File’ actions, and turn on the ‘Ask Where To Save’ button.
Click on the Shortcut settings (top right button) and turn on the ‘Show in Share Sheet’ option (give it a name and a unique icon while you’re there, too).
From then on, all you have to do is long press a zip file and choose Share> Shortcuts>Your Shortcut to unzip a file wherever you want (I tend to use the Scrivener folder on my iPad).