Using n'a pu in spoken French would be extremely formal and surely surprise the person listening. We essentially always say n'a pas pu or better a pas pu in most occasions.
On the other hand, dropping pas in written French (at least in France but I don't think there are regional differences) is still very common and unsurprising to me. What used to be rare was using pas with pouvoir, and while the difference lessens, it is still rarer that the shorter form according to Google Books:
Only a few verbs are subject of this frequent omission, they are cesser, oser, pouvoir and savoir according to the OQLF BDL:
Bien que l’adverbe de négation ne soit généralement employé avec un autre adverbe de négation, il est possible, dans certains contextes, de l’employer seul. Il en est ainsi avec les verbes cesser, oser, pouvoir et savoir, principalement lorsqu’ils sont suivis d’un infinitif.
With other verbs, the form with pas took the lead a while ago, e.g.:
There are gazillions of hits with n'a pu se rendre and I'm sure many parents are using this form when writing mots d'excuse to their child's school. No technology bias involved here.
Nevertheless, the trend is in favor of the form with pas so the degree of familiarity with it likely increases within the younger generations.