Missing KDE4 Dolphin "Service Menu / Actions" menu entries in Plasma5 desktop?

All of my Dolphin plugins didn't show up on Dolphin anymore even if they were placed in the right folder: /usr/share/kservices5

Most of those KDE4 era plugins are actually Konqueror plugins. You can find that by opening the *.desktop files of plugins that are not visible in text editor.

[Desktop Entry]
Type=Service
X-KDE-ServiceTypes=KonqPopupMenu/Plugin
MimeType=video/*
Actions=DownloadSub

[Desktop Action DownloadSub]
Type=Application
Name=Subliminal subtitle search
Exec=subliminal download -m 0 -l en fi -- %U
Icon=video

To get those working again you need just:

sudo cp /usr/share/kde4/servicetypes/konqpopupmenuplugin.desktop /usr/share/kservicetypes5/