trash:/-protocol is currently broken on Windows: https://bugs.kde.org/show_bug.cgi?id=414430
The cause seems to be that the trash-protocol meta data is not installed on Windows: The protocol is
built from entirely separate sources on Windows, and the Windows-version was forgotten in this commit:
https://cgit.kde.org/kio.git/commit/src/ioslaves/trash/CMakeLists.txt?id=a3fee508c6c42b1b86155719e38a84b1128360eb