For whatever reason the problems largely centre on UK airports and UK-based aircraft.
Brexit may be an additional factor at Palma as you stated, but the article says this:
All over Europe, airports are suffering from horror delays, as many people take overseas holidays for the first time since the onset of the pandemic and airlines struggle to fill staffing shortages. “Pent up demand” is leading to an airline booking surge, explained Olivier Jankovec, Director General of Airlines Council International Europe. “At the moment, the performance of passenger traffic is trending along our high-case optimistic scenario on the back of travel restrictions lifting across many markets,” he said. According to ACI modelling, delays and cancellations are inevitable at two thirds of European airports this summer.
Doubt whether the additional checks needed on the increased number of non-EU pax is that widespread, unexpected demand levels seems a bigger factor