@Matthew J It seems incredible that flicker on windows is still a thing these days.
It has nothing to do with modernity, it has everything to do with Windows itself. And, additionally, with the hardware platform. Mac has screen double buffering in hardware, that is not the case for most every graphic card on PC.
As a developer, you should take into account the hardware and software platform.
My app Watermark on Mac uses several canvases and does not flicker any single bit.
On Windows, the very same source produced an app which was simply unusable since it flickered like fireworks. I refactored it to use a single canvas, and it does not flicker more than the Mac version, meaning not at all.
I do spend most of my development time on Mac, but I always make sure to do the last mile on a regular PC, to make sure my customers will have the best user experience. Unfortunately, Xojo's promise of "develop once, compile many", cannot be fulfilled when one platform allows stacking controls, and the other not.
A lot of Xojo developers develop on Mac and generate apps for Windows and Linux that they run in VM, so they have no idea that on a regular PC, their apps become flickery and don't look professional.
The other way around, an app produced on Windows and carefully tuned to avoid flicker will generate Mac and Linux executables which will be as smooth as silk.