Unable to use any Paraview Filters

Hi everyone,
I am a new user to LIGGGHTs and Paraview. I am using Ubuntu 20.04, LIGGGHTS version 3.8.0 and Paraview 5.8.0.
After running my simulation, I used lpp to convert my files to VTK successfully and then I loaded into Paraview. However, when I tried to use Paraview Filters, I cannot choose anything options because all the filters are greyed out.
Can anyone have any ideas about how to fix this issue?
Any ideas would be highly appreciated.
Thao