Errors on Startup and Missing Configuration Interface Elements

[Polaris]

I.Error messages on startup:

A. From GUI:
1. When start it for the first time, get the prompt to use OpenGL or not.

2. On every boot:
"No plug-ins were found.
Plug-ins provide most of the functionalities (animations, applets, views, etc.)
See http://glx-dock.org for more information.
There is almost not meaning in running the dock without them and it's probably due to a problem with the installation of these plug-ins.
But if you really want to use the dock without these plug-ins, you can launch the dock with the'-f' option to no longer have this message."

B. From terminal:
y@P2:~$ cairo-dock
warning : (/build/cairo-dock-XfXg2O/cairo-dock-3.4.1/src/implementations/cairo-dock-egl.c:gldi_register_egl_backend:232)
  Cairo-Dock was not built with EGL support

(cairo-dock:3481): Gtk-WARNING **: 13:25:41.979: Theme parsing error: gtk.css:63:28: The :prelight pseudo-class is deprecated. Use :hover instead.

(cairo-dock:3481): Gtk-WARNING **: 13:25:41.979: Theme parsing error: gtk.css:73:35: The :prelight pseudo-class is deprecated. Use :hover instead.

(cairo-dock:3481): Gtk-WARNING **: 13:25:41.979: Theme parsing error: gtk.css:115:31: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(cairo-dock:3481): Gtk-WARNING **: 13:25:41.979: Theme parsing error: gtk.css:116:24: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(cairo-dock:3481): Gtk-WARNING **: 13:25:41.979: Theme parsing error: gtk.css:145:27: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(cairo-dock:3481): Gtk-WARNING **: 13:25:41.979: Theme parsing error: gtk.css:146:29: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(cairo-dock:3481): Gtk-WARNING **: 13:25:41.979: Theme parsing error: gtk.css:166:34: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(cairo-dock:3481): Gtk-WARNING **: 13:25:41.980: Theme parsing error: gtk.css:187:34: The :inconsistent pseudo-class is deprecated. Use :indeterminate instead.
warning : (/build/cairo-dock-XfXg2O/cairo-dock-3.4.1/src/implementations/cairo-dock-glx.c:_initialize_opengl_backend:129)
  couldn't find an appropriate visual, trying to get one without Stencil buffer
(it may cause some little deterioration in the rendering) ...

 ============================================================================
 Cairo-Dock version : 3.4.1
 Compiled date : May 24 2018 23:52:39
 Built with GTK : 3.22
 Running with OpenGL: 1
 ============================================================================

g_file_test: assertion 'filename != NULL' failed
g_file_test: assertion 'filename != NULL' failed

(cairo-dock:3481): Gtk-WARNING **: 13:25:42.649: Theme parsing error: <data>:7:1467: The :insensitive pseudo-class is deprecated. Use :disabled instead.

(cairo-dock:3481): Gtk-WARNING **: 13:25:42.650: Theme parsing error: <data>:7:3649: The :inconsistent pseudo-class is deprecated. Use :indeterminate instead.

*** Note: debug.txt attached

II. Missing Configuration Interface Elements.

In: -Cairo-Dock>Configure>Appearance>Docs>Views tab>Main Dock: "3D Plane" option is missing
                                                   >Sub-Docks: "Slide" option is missing
    -Cairo-Dock>Configure>Appearance>Docks>Slide tab is missing
    -Cairo-Dock>Add>Applet>Files>"Bin and Folders" is missing (*** therefore can't add ***)
    -Sub-dock>Edit>Extra Parameters: view with "rows" of icons missing

III. System Specs.

Cairo-Dock version: 3.4.1 (installed from "Software" repository)
Am using OpenGL.
Linux: Xubuntu 20.04 64bit
Desktop Environment: XFCE
Window manager: xfwm4 4.14
Themes: Greybird, Greybird-dark (either - same result)
Graphic card: Gigabyte HD6870 - powered by AMD Radeon HD 6870 GPU
Drivers and other graphics info:
-Display-
Resolution : 1920x1080 pixels
Vendor : The X.Org Foundation
Version : 1.20.8
-OpenGL-
Vendor : X.Org
Renderer : AMD BARTS (DRM 2.50.0 / 5.4.0-37-generic, LLVM 9.0.1)
Version : 3.1 Mesa 20.0.4
Direct Rendering: Yes

[Fabounet (fabounet03)]

Hi,
It seems the plug-ins are not installed, or installed with a different version. ( "No plug-ins were found").
See if you can install the cairo-dock-plug-ins package.