Hey Pascal:
You seem to have learned quite a lot about this problem of Sweet Home 3D not launching in Ubuntu.

When I run it to terminal here is what I get:

Java 3D: implicit antialiasing enabled
Java 3D ERROR : GLX extension is not supported
GLX version 1.3 or higher is required
Gtk-Message: 23:46:53.643: Failed to load module "canberra-gtk-module"
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
etc.

I have Java Oracle 12 installed. What is this GLX 1.3 and how do I fix it? I cannot see it in my system.