That must be recent, as it certainly was not the norm in the UK even prior to Brexit. For some medicines, UK pharmacists are required to split packs as needed to give exactly the number of pills prescribed.
I can't find anything to suggest EU rules prevents split packs - I do see there was a tightening of the rules on how to treat packs if dispensing split backs a few years ago, but nothing since. Do you have a source?
EDIT: At least as late as per the False Medicines Directive going into force in 2019, split pack dispensing was explicitly allowed - the FMD set out rules for the controls required to do so. E.g. the original container can not leave the dispensary until its entire content is used, and the pharmacy can't re-sell or supply other pharmacies with it.
[In fact, I just got a prescription filled and received 12 pills in a pack consisting of one full blister pack and a carefully cut out piece with 2 pills; but again in the UK so it could be there are newer EU regulations though I haven't seen any]
