Also, apple's app store is famously LGPL-incompatible.
If you're shipping a proprietary application that links to LGPL libraries in accordance to the license, that's fine.
It's GPL applications that the App Store bans.
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++ :)
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.
It all works very nicely.
I dumped GTK a few years back due to - and I have no idea if the same thing happens today - weirdness with GTK themes not working between minor releases of it, and I vaguely remember there were other annoyances but by then I was impressed with Qt and the PySide (noe PySide2) bindings so stuck with it.