Steps to Reproduce

download the image from https://www.zkoss.org/zkdemo/file_handling/file_download

Actual Result

on iPad (iOS 9.3.5) download works as expected
on iPad mini: popup warning is displayed, download continues after allowing
on iPhone: no warning at all download is ignored

Expected Result

working download (within the usual limitations of iOS devices)

Debug Info

• using chrome on iOS there is no such issue
• iPhone 8 Plus, iOS 15.2.1 still has the bug

Root Cause

iOS' popup blocker is enabled by default blocking downloads triggered from the server side.
disabling the popup blocker will give the user the option to "allow" the popup/download.

Workaround

use direct download links instead
https://www.zkoss.org/javadoc/8.0.0/zk/org/zkoss/zk/ui/Desktop.html#getDownloadMediaURI(org.zkoss.util.media.Media,%20java.lang.String)
or
https://www.zkoss.org/javadoc/8.0.0/zk/org/zkoss/zk/ui/Desktop.html#getDynamicMediaURI(org.zkoss.zk.ui.Component,%20java.lang.String)