Blocked taskbar behavior after maximizing
After setting the taskbar to automatically hide, maximize the window, and then move the mouse to the bottom of the screen, the taskbar does not pop up.
If other applications are maximized, the taskbar will pop up.
I think that's because windows treats any "popup" window that covers the entire screen (with no non-client area on screen) as a full-screen window (like a game in a borderless window).
Looking at the Discord app and Fork shows that when maximized,
these do not cover the entire screen -- they leave one or two pixels uncovered at the bottom of the screen.
Also, they do not use the WS_POPUP style, maybe they are doing something more like Custom Window Frame Using DWM.
However I'm not exactly sure how to accomplish that in practice.
Using SetWindowPos to make the window a bit shorter when it gets maximized works,
but only if it's much shorter (leaving a gap of 10-20 pixels).