I wouldn’t say all of the privacy changes or even the majority of them are to ensure lock-in, but they have certainly been using their privacy stance as a pretext for lock-in.
There's no way to do this, even if you pay all the fees push notifications won't work unless you publish to the app store and that will get rejected for being a duplicate.
That being said, I don’t think Apple’s privacy stance is all hot air, they publish plenty of white papers on their infrastructure. I mostly think they’re greedy and don’t mind harming the user and developer experience to ensure they get their cut from every transaction that occurs inside their ecosystem.