As a specific registered user by ("user name" or "user id") in the account when adding an ad, hide a certain category in the drop-down list - for example (hide for a user with ID - 9 category <option value = "4"> Cars </option>).

@Олег Котел
Only option would be to do it via jQuery

Can you set an example?
I'm not very good at jQuery.
Thanks.

Thanks for the quick response.

As I understand it, 'X' is the category id, in my case it is "4" (<option value = "4"> Cars </option>). And how to set user id "9" which does not show this field? And where to write it in (functions.php)?

Thanks again!

You put block into PHP condition for user id... if osc_logged_user_id() == 5...

I was already confused, I did not understand what the full code should be! If you can, then please complete the full code ...
I will be very grateful.

Thanks a lot, everything works great ...