The linked press release has a whole section explaining how get got to the fine https://ec.europa.eu/commission/presscorner/detail/en/ip_24_...
> In addition, the Commission decided to add to the basic amount of the fine an additional lump sum of €1.8 billion to ensure that the overall fine imposed on Apple is sufficiently deterrent. Such lump sum fine was necessary in this case because a significant part of the harm caused by the infringement consists of non-monetary harm, which cannot be properly accounted for under the revenue-based methodology as set out in the Commission's 2006 Guidelines on Fines.