Created attachment 456286 [details] kwin-wayland-run Please, add missing qtvirtualkeyboard dependency for kde-plasma/kwin:5 with USE="app". Unfortunately, qtvirtualkeyboard is not in the tree. https://download.qt.io/official_releases/qt/5.7/5.7.1/submodules/qtvirtualkeyboard-opensource-src-5.7.1.tar.xz
s/with USE="app"//
I'm running into the same problem trying to run kwin_wayland.
dev-qt/qtvirtualkeyboard was added to tree in git commit 96970cfb33aedf2a831813e48fb722e4b54acf77. kde-plasma/kwin will start to depend on it with 5.11.0.