I've found the answer.
When enabling mount.cifs debug mode (echo 3 > /proc/fs/cifs/cifsFYI), we can see errors in the dmesg output :
# dmesg
[ 7845.389949] fs/cifs/xattr.c: CIFS VFS: in cifs_getxattr as Xid: 50 with uid: 0
[ 7845.389953] fs/cifs/xattr.c: illegal xattr request security.selinux (only user namespace supported)
[ 7845.389956] fs/cifs/xattr.c: CIFS VFS: leaving cifs_getxattr (xid = 50) rc = -95
[ 7845.389964] fs/cifs/xattr.c: CIFS VFS: in cifs_getxattr as Xid: 51 with uid: 0
[ 7845.389967] fs/cifs/xattr.c: CIFS VFS: leaving cifs_getxattr (xid = 51) rc = -95
so using the parm nouser_xattr fix the issue :
$> mount -t cifs //192.168.224.1/MYSHARE$ TEST -o username=admin,uid=10066,gid=10000,dir_mode=0755,nouser_xattr --verbose
$> ll .
drwxr-xr-x 1 admin utilisa._du_domaine 0 jun 11 17:14 TEST