* I never said all software handles the swapchain itself. The front and back buffers are obviously not usually allocated in user code. But they're allocated nonetheless and contributing to memory usage.
* Not every app is fullscreen, but I was using a maximized app as an example. If you make the window smaller then yeah obviously the numbers get smaller proportionally.
* A ton of people have 4k displays, it's difficult to find a moderately high end laptop without a 4k display these days. In any case, that was the hypothetical example I used.
* If you have a window that's roughly 4k resolution, and you want a background picture which fills the entire window, that's gonna be a roughly 4k resolution pixel buffer (unless you stretch a smaller image, but that looks ugly).
* Depends on the text renderer. I have mainly used pangocairo, which is based around CPU rendering text to a pixel buffer. I know that this is the typical recommendation for handling high quality rendering of longer pieces of text with Canvas on the web too. Maybe a typical win32 app actually does render each glyph fresh every frame from a font atlas, I'm not familiar with Windows APIs specifically. I apologise for the inaccuracy if that's the case.
* I'm pretty sure you're wrong here? If DWM has only one buffer which all windows share, how does it handle the case where a partially obscured window goes unresponsive for a bit as the user removes what obscures it? In old school non-composited X11, the answer is that the X server paints in the newly revealed area with grey pixels and asks the window's process to re-render that region, causing a lingering grey region if the app is frozen. Preeeetty sure that Windows 11 doesn't do that. But do you have documentation on this?