Install libplank1 by entering the following commands in the terminal:
sudo apt update sudo apt install libplank1
Library to build an elegant, simple, clean dock
Plank is a dock enabling you to start applications and manage your windows. . Plank is meant to be the simplest dock on the planet. The goal is to provide just what a dock needs and absolutely nothing more. It is, however, a library which can be extended to create other dock programs with more advanced features. . This package contains the shared library used by docks based on Plank.