Thanks for reaching out to us about this. The "Sync to iOS" option mentioned in the release notes refers to the "Sync to iPhone or iPad..." option in the Export Document menu of the macOS version of VoodooPad 5. This option, which synced documents over local wifi, is no longer available in VoodooPad 5.2.0 in favour of syncing via Dropbox. By focusing on syncing via Dropbox, our goal is to make syncing VoodooPad documents between devices more stable and consistent going forward.
If you have any other questions, please don't hesitate to let me know.