I have the exact same problem.
I want to uninstall the HD pack for Shadow of Mordor and I can't...
Edit:
By going to the "properties" window of the game, we can access the dlc tab.
It works for me on Fedora 30 with GNOME. I was able to start downloading the HD pack, cancel it, and then start it again.
To be clear, this was via the Manage My X DLC button, not the properties window.
It's strange, I'm also on fedora 30 with gnome...
The manage DLC button is now working properly with the library beta build from Oct 30.
Nothing extracted yet.
Your system information
Please describe your issue in as much detail as possible:
Clicking the "Manage My x DLC" button does nothing. On the Windows client it opens a new window for managing your DLC.
Steps for reproducing this issue: