If themes are not appearing after installation, some users have found success by checking for multiple versions of (a scripting addition cDock relies on) across different /Library/ScriptingAdditions directories and ensuring only one copy remains.
The 4.5.0 update focused heavily on expanding themeable elements and addressing stability issues introduced by macOS Big Sur: cDock 4.5.0
: Users can now theme both the empty and full states of the Trash can and set a custom sound for emptying it. If themes are not appearing after installation, some
: Several critical bugs were addressed, including Dock freezing when dragging items in Big Sur and various crashes when switching themes or editing settings. cDock 4.5.0