gestion users / categories

Did you try not giving your users this FLEXIcontent ACL permission:

Items (Backend Tab): Display all
Allow users in the group to list all Items (in items management), otherwise the user will only see the items that he/she can edit.

-- Remove this from the user groups and backend users will be able to see only items that they can edit

yes this is what I thought, but, If I denied it I have this error :

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 72 bytes) in /path..../libraries/joomla/access/rules.php on line 107

I will check this locally , reproduce and fix it

How many items (articles) do you have totally ?

1755 for this user and this is just beginning...

and totally for this site?

119 pages of 20 items >> 2380

Idea is that this user wil upload much more articles by import function and will manage it. So it will grow...