How to get your Linux Mono version 'complete' and 'up-to-date'

(The following is especially important for Linux users that experience errors when running WG++)
The last wg++ versions, from V3.2 onwards require a 'complete' and 'uptodate' mono version, it needs :

Mono-complete 6.12.0.122 or higher

(!! Mono-devel is not good enough .. and it is not always easy to know if you have Mono-complete or Mono-devel )

The following steps solved the 'problem' on two computers ;
.. A laptop with mono 6.8.0 which was 'cured' with the steps in 1. 
and 
.. A desktop on with mono-devel 6.12.0.122 on it with the steps in 2.

Step 1. Check the version 
.. Do this :
sudo mono --version
.. It's OK if the first line reads, (or higher): 
Mono JIT compiler version 6.12.0.122 (tarball Mon Feb 22 17:33:28 UTC 2021)

.. If this is not OK follow the steps in 
https://www.mono-project.com/download/stable/#download-lin 
.. for the last step 
.. install mono choose !! :
sudo apt install mono-complete

.. Check version again 
.. If OK now try running WG++ using the run script from your wg++ homefolder do :
sudo ./run.sh 

.. If that still fails ..

Step 2. Uninstall / Reinstall Mono
.. Do this :
sudo apt remove --purge --auto-remove mono-devel
.. and just to be sure also :
sudo apt remove --purge --auto-remove mono-complete
sudo apt remove --purge --auto-remove mono-runtime

.. Make sure all is gone with (must show nothing !):
sudo mono --version    

.. Then 
sudo install mono-complete
.. check version again 
sudo mono --version 
.. Must be , this or higher :
Mono JIT compiler version 6.12.0.122 (tarball Mon Feb 22 17:33:28 UTC 2021)

run WG++ 

and .. hopefully .. happy grabbing again