iOS behaves oddly when you have more app than fit on the 11 allowed homescreen pages. Additional apps are installed. You can find them by searching. But you can’t see them on the home screen, and thus you can’t delete them.
What’s worse, is that making room on the final home page still doesn’t show these icons. If you delete/move say 8 apps from the last page you will have 8 gaps. Only when you install a new app (if you’re a dev, e.g. by XCode), will the hidden apps use up the available space.