'iOS files' in storage

I presume you see this in System Settings > General > Storage.

iOS backup can be located like this:

Locate backups of your iPhone, iPad, and iPod touch - Apple Support

Using the Finder > Go menu > Go to Folder method, you may also find iOS software updates in ~/Library/Application Support/MobileSync

iOS (iPhone, iPad) device backups, probably. You can delete them if you so choose.

Post the fully qualified pathname to be sure. To determine it, two-finger tap the filename, choose "Copy <...> as Pathname" and post it here if you wish. Please redact your user name; the beginning part e.g /Users/john/ which we don't need to know.

Yes, thanks. You can delete that backup if you so choose. Click the "Verwijder" (Delete) button, and confirm the dialog that appears next ("Are you sure you want to delete ...").