Description of problem:

In the Advanded Settings interface ("Tweak Tool") the "Shell Theme" button (in the "Appareance" index) does not allow to select the folder where the user themes are stored and as a result no customized theme can be used .
(this button is available after installing and activating the "User Themes" shell extension) : a selection windows is opened and it allows to browse through the tree structure but it doesn't allow to make a choice .  

Version-Release number of selected component (if applicable):
- Mageia 6 64 bits installed from the Live ISO and updated ;
- GNOME 3.24.2

How reproducible:
. Permanent.

Steps to reproduce :
1. Install and activate the "User Themes" Gnome extension from the site https://extensions.gnome.org/ ;
2. Open the "Advanced Settings" interface ;
3. In the first index, try to select any user's folder with the "Shell Theme" button. In my environment that doesn't work.