With the BIG Icons app, you can place icons/tiles of various sizes on your homescreen(s). That’s not where the story ends, though. These are not just big app icons that you can tap, no, not at all.

On the other hand, if you want to replace the app icon with your own image -- or you don't have iOS 18 -- you'll have to use the Shortcuts app. How to customize an app's icon using the Shortcuts app ...