Install libgnustep-gui0.26 by entering the following commands in the terminal:
sudo apt update sudo apt install libgnustep-gui0.26
Description:
GNUstep GUI Library
The GNUstep GUI library is a powerful library of graphical user interface classes written completely in the Objective-C language; the classes are based upon the OpenStep specification, and provide the user with a traditional nextstep-like look and feel. The classes include graphical objects such as windows, menus, buttons, text fields, popup lists, browsers, scrollviews, splitviews, fonts, colors, images, events, pasteboards... You need the corresponding backend library package (gnustep-back) to use this package.
Homepage: http://gnustep.org
Version: 0.26.2-3
Section: universe/libs