All written in Python, recently moved to Qt5 and PySide2, runs on Windows and when I figure out packaging for Linux (probably AppImage) will release it for Linux as well.
I believe there are Qt bindings for other languages too.
I like that UI! Out of curiosity, do you use a kind of wysiwyg (a la qt designer) to make your interfaces, or do you write Python code directly? Coming from JavaFX using scenebuilder to design UIs, l tried Pyside2 some years ago, never managed to find a way to make it work with a wysiwyg the way I am used to with JavaFX. Writing and styling widgets by hand is painfully slow.
I use Qt Designer for the layout. I never could get the hang of the Horizontal & Vertical spacers or the Layout Managers in Qt, so it's a static layout.
There are quite a few "pages" in the application which appear or disappear when required. Those are all QWidgets which have their own static layout.
The doughnut chart showing materials available on a planet is a dynamically created web page shown via a QtWebView widget.
There's an Overlay Widget which is basically a QWidget with transparency, with the main window being hidden then called up via a global hotkey - I use Python ctypes to enable the global hotkey, calling the Windows API to enable that functionality.
And the underlying databases used are sqlite3 via SQLAlchemy.
All written in Python, recently moved to Qt5 and PySide2, runs on Windows and when I figure out packaging for Linux (probably AppImage) will release it for Linux as well.
I believe there are Qt bindings for other languages too.
So you're not stuck with C++ :)