Using konqueror 17.04.0 with WebEngine part on openSuse 42.2, Qt 5.8.0 when browsing youtube.com I can not switch the videos to fullscreen mode. Clicking on the fullscreen icon in the video pops up a tooltip saying "Full Screen is unavailable" Why ?
This works with Falkon and as far as I know it uses same webengine renderer, so there may be some tweak or something that Konqueror is missing. It would be great if that tweak is ported from Falkon to Konqueror.
Full screen mode should work in 20.12: https://invent.kde.org/network/konqueror/-/merge_requests/12/diffs