So which plugins are installed then?
Does you plugin directory look something like this:
~/Apps/ParaView-5.6.0-MPI-Linux-64bit/lib/plugins$ tree
.
├── platforminputcontexts
│ └── libcomposeplatforminputcontextplugin.so
├── platforms
│ └── libqxcb.so
├── sqldrivers
│ └── libqsqlite.so
├── VCGCriticalPointsPlugin.so
├── VCGFlowMapGradientPlugin.so
├── VCGModelPlugin.so
├── VCGModulePlugins.so
└── xcbglintegrations
└── libqxcb-glx-integration.soThanks a lot, Louis @louisgag.
What I did was just mv ./vcgparaview_plugins/* <paraview_path>/lib/plugins. I think I should have copied the vcgparaview_plugins/lib/* and vcgparaview_plugins/lib/plugins/* into ~/ParaView-5.6.0-MPI-Linux-64bit/lib/plugins. Now I have all the VCG*.so in ~/ParaView-5.6.0-MPI-Linux-64bit/lib/plugins/. Do I need to load them manually? Because even now, they are not in my local plugin lists when I open Tools → Plugin Manager.
It looks like the instructions on the website are wrong.
The correct command would be mv ./vcgparaview_plugins/* <paraview_path>, i.e., copy the contents of vcgparaview_plugins/lib to <paraview_path>/lib.
Relative to ParaView’s path, the files libXXX.so need to be in the lib/ directory, and the plugins VCGXXXX.so in the lib/plugins/ directory. If done correctly, the plugins are loaded automatically.
Thank you for your reply and sorry for the trouble @lhofmann. I did as you said. I even followed the “Archive” instruction on the website which has the plugins and libs in the correct directory, yet I still don’t see the plugins when I open the ParaView. I cannot load them manually either, I get this error:
libOpenGL.so.0: cannot open shared object file: No such file or directory
ERROR: In /home/buildslave/dashboards/buildbot/paraview-pvbinsdash-linux-shared-release_superbuild/build/superbuild/paraview/src/ParaViewCore/ClientServerCore/Core/vtkPVPluginLoader.cxx, line 403
vtkPVPluginLoader (0x7f617000cf10): libOpenGL.so.0: cannot open shared object file: No such file or directory
I’ll try to see if I can install it using the “Debian Package VCGParaView” instruction.
You could try installing the libopengl0 package: sudo apt install libopengl0
Thank you @lhofmann. Installing the libopengl0 solved it. I really appreciate your help. 
Hi @lhofmann
I am trying to solve ftle field for some complex 3d geometries. Are these paraview plugins able to calculate ftle in 3d complex shapes? or are they just for simple 2d shapes? I highly appreciate your answer on this. Thanks a lot in advance.