I have a Nexus 5 with Ubuntu-touch 16.04.
I mistakenly removed the Desktop Apps app. I can't install it again, because the open store says that my phone doesn't support the app.
So how can I run Linux GUI apps, with libertine or natively?
You do not need to install the scope separately any more. If you open the scopes overview/manager by swiping up from bottom edge on the dash, you can favorite the already installed desktop apps scope, to see the list of apps in your libertine containers again.