As far as I can tell this basically means that all apps must be approved by Apple to follow their “platform policies for security and privacy” even if publishing on a third party app store. They will also disable updating apps from third party app stores if you stay outside the EU for too long (even if you are a citizen of an EU country, with an Apple account set to the EU region).
The idea that preventing app updates is in line with their claims of protecting security is utterly absurd. “Never attibute to malice what can be explained with stupidity,” but Apple isn’t stupid.
Gatekeepers and the DMA, are not exactly antitrust laws; they are a series of regulations applied to entities providing a digital service to above roughly 10% of the EU population, no matter the market share, without provisions to break them up.
I guess… you could call them “antitrust light”, sort of.