How to fully disable android, iOS & desktop app?
See this existing thread for some pointers how to restrict access to ownCloud:
Thank's for answer, but owncloud is installed without Active Dirrectory support, LDAP module is disable now.
Maybe it can be done with rewriting php functions?
Sure, ownCloud is written in PHP and open source so you're able to rewrite anything in the code itself. So you need to have PHP knowledge and be able to find that code and remove it. However by removing that part in the personal info users will still be able to use the apps.