When is there a need to open and handle a complaint?

Hello,

first of all thank you, that you offer this service and even free of charge!

I have more or less a simple question:
Does a complaint only begin when a company receives a complaint from a customer ( oral, written or electronic) OR also when a customer reports a case to a service hotline, e.g. if the medical device is not working properly and the service team can fix the problem - but there might be a problem with the device in general that needs to be investigated?
In the latter case, the company itself would initiate the complaint, but I wonder if this is even necessary because it was not officially reported by a customer?

I hope if it is clearly to understand what I mean.. :)