This is exactly why I used TOTAL to ignore the dimensions displayed in the chart but to take into account the dimensions in the selections.
What I don't understand is why when I add TOTAL to the expression, it displays dimension values that are not linked to any fact (in my model there is not a single fact linked to the value Composant).
Removing blank Category is easy - check "suppress when value is null" on the Dimensions tab.
'Composant' is a different story. You didn't see it in the first table (no total) apparently because "suppress zero-values" is checked on the Presentation tab. If you want to remove it, you need a condition for the "total" column, or maybe better to use calculated dimension in this case, like this: