Reading the release notes, it seems that now you can choose the rendering mode (at least with pvbatch) with the --opengl-window-backend but I’m wondering if the official 6.0RC3 has this capability or if that’s available only if you recompile paraview activating EGL support.
It’s available in the official releases, and it is possible with pvbatch and pvserver. Note that there are no longer separate Linux server for headless rendering with 6.0.0, but rather one package that will use OpenGL with X if it is available, EGL without X if it is available, and fall back to osmesa if neither is available.