Instructions for installing Qt and Qt Creator on Linux

Getting started with Qt and Qt Creator on Linux

https://www.ics.com/blog/getting-started-qt-and-qt-creator-linux

step 1: $ sudo apt-get install build-essential libgl1-mesa-dev

step 2: sudo apt install gdb

step 3: 
$ cd ~/Downloads
$ chmod a+x qt-unified-linux-x64-2.0.3-1-online.run

step 4:
version user installation:
$ ./qt-unified-linux-x64-2.0.3-1-online.run

global installation (all users)
$ sudo ./qt-unified-linux-x64-2.0.3-1-online.run

Troubleshooting:
“Failed to load platform plugin ”xcb“ ” 

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

Aborted (core dumped)


Solution:
$ sudo apt-get install libxcb-xinerama0

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  chromium-codecs-ffmpeg-extra gstreamer1.0-vaapi
  libgstreamer-plugins-bad1.0-0 libva-wayland2
Use 'sudo apt autoremove' to remove them.
The following NEW packages will be installed:
  libxcb-xinerama0
0 upgraded, 1 newly installed, 0 to remove and 244 not upgraded.
Need to get 5.260 B of archives.
After this operation, 37,9 kB of additional disk space will be used.
Get:1 http://ro.archive.ubuntu.com/ubuntu focal/main amd64 libxcb-xinerama0 amd64 1.14-2 [5.260 B]
Fetched 5.260 B in 0s (42,8 kB/s)     
Selecting previously unselected package libxcb-xinerama0:amd64.
(Reading database ... 184329 files and directories currently installed.)
Preparing to unpack .../libxcb-xinerama0_1.14-2_amd64.deb ...
Unpacking libxcb-xinerama0:amd64 (1.14-2) ...
Setting up libxcb-xinerama0:amd64 (1.14-2) ...
Processing triggers for libc-bin (2.31-0ubuntu9.2) ...