Once upon a time, Chromium had a bug where using $mod+f in i3 to fullscreen the Chromium window changed the window to occupy the entire screen, but didn’t actually make Chromium enter full screen mode. Watching 4 YouTube streams in parallel was still possibly, back in those days: When executing the second command while the chromium window is focused, the chromium full screen state will be completely detached from the the Sway full screen state.