[bsimpson]

The DMA is enforced by bureaucracy. The commission proposes that certain platforms are big enough to be regulated, and then there's a comment period/negotiation. The list of platforms currently being regulated is publicly available.

[bootsmann]

There is a hard number of users you have to achieve, its one of the reasons why iOS had to allow third party app stores but playstation did not.

[arter45]

In fact, Apple is still part of the DMA list with Safari, iOS, iPad OS and App Store.