Probably this information will help. I was on Ubuntu 18.04 and when I tried to install Krita, using the ppa method, I got this error:

This application failed to start because it could not find or load the Qt platform plugin “xcb” in “”.

Available platform plugins are: linuxfb, minimal, minimalegl, offscreen, wayland-egl, wayland, xcb.

Reinstalling the application may fix this problem.

Aborted

I tried all the solutions that I found in this thread and other webs without any success.

Finally, I found a post where the author mention that is possible to activate the debugging tool of qt5 using this simple command:

export QT_DEBUG_PLUGINS=1

After adding this command I run again krita I got the same error, however this time I knew the cause of that error.

libxcb-xinerama.so.0: cannot open shared object file: No such file or directory.

This error prevents to the “xcb” to load properly. So, the solution will be install the `libxcb-xinerama.so.0″ right? However, when I run the command:

sudo apt install libxcb-xinerama

The lib was already installed. Now what Teo? Well, then I used an old trick 🙂 Yeah, that one --reinstall

sudo apt install --reinstall libxcb-xinerama

TLDR: This last command solved my problem.