iOS app version 0.1(27) It does not make much sense to download a file with a mobile device (i.e. the file is on the device or in iCloud). Nevertheless, the File - Download as menus do nothing. The HideExportOption WOPI property would hide the menu, but it would also disable the full screen presentation mode, which is working on iOS.
Tor Lillqvist committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/online/+/54951870c3ed7c7f128d53449b4b0f77126117a8%5E%21 tdf#124448: Don't show the 'Download as' menu entry on mobile apps
Fixed in master and collabora-online-4.
*** Bug 124159 has been marked as a duplicate of this bug. ***