I was wondering whether it is possible to completely disable a function that is called in a parent theme's
functions.php and if so, how? (Of course without deleting the function. Rather by adding something to
functions.php of the child theme.)
Only under some circumstances.
Those are the cases I can think of right now. Perhaps I have forgotten a case. I trust someone will point that out if I have :)
There is no PHP level "remove function" and if you try to define two functions with the same name you will get an error.
As I can't see the code for the function you want to remove, I worry that you are going to break something by removing or altering it, if that is even possible. A little caution is in order.
While it's difficult to know exactly how to do what you want without seeing code, this may help - How to override parent functions in child themes?
Just ignore the override part of that Q&A if you're not interested in altering the function, and focus on how it goes about removing it.
Basically, you'll want to use use remove_action or remove_filter in your child theme's