After following the instruction to make a clean install, the issue still persits.
If I may add some information:
The enable/disable of Define card by clicking in the boxes in the Run tab works correctly from the input file point of view, the problem is just that the box does not get visually “ticked/unticked”.
If I downgrade to a previous version of Flair 3.1-5, the problem no longer occurs
This visualization issue occurs when using Ubuntu 18.04 with WSL. When testing Flair 3.1-6 on another machine with Ubuntu 18.04 as OS everything works fine (the boxes are fully filled when ticked)
This box tick issue visualization also occurs with other boxes like the ones to customize the layers in the Geometry tab (see boxes circled in yellow in the image below). The other boxes such as the “Global” tick box in the picture below are correclty visualized when ticked.