Zenity is not available for Mac but there are some alternatives that runs on macOS with similar functionality. The best Mac alternative is wxGlade, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to Zenity and seven of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to Zenity are wxFormBuilder (Free, Open Source), CocoaDialog (Free, Open Source), Dialogblocks (Paid) and PyDialog (Free, Open Source).
wxGlade is a GUI designer written in Python with the popular GUI toolkit wxPython, that helps you create wxWidgets/wxPython user interfaces. At the moment it can generate Python, C++, Perl, Lisp and XRC (wxWidgets' XML resources) code.
Anthemion DialogBlocks is a sizer-based resource editor that quickly gets you creating professional-looking dialogs, wizards and frames for deployment on Windows, Linux, Mac or any other supported wxWidgets platform.
My problem was that the KDialog code is still not ported to Qt5 and it depends on various Qt4/KDE4 components. The kdialog has big dependency sizes so we made an alternate dialogs like kdialog switches, options.