Again, I don't expect them to do this. But they could add a useful level of trust if they were really motivated to do so.
As for no company giving up rights, I did say I didn't expect Apple to actually do this, only that they could. Though, companies do actually make binding contractual promises all the time. It's just that they don't tend to do it with consumers or small businesses who have no negotiating leverage and/or no desire to insist on those promises.
Regarding your hypothetical, anything that's actually legally mandated by the government generally overrides contract law since the courts won't enforce illegal contracts and illegality is a defense to breach of contract. They can always do what the law actually requires.
But we're not talking about the government mandating things, since both the iOS 14 behavior and the iOS 15 behavior comply with the law.
Which means this action is just a charade, as I pointed out. Because fundamentally it doesn't really matter. The gov is going to do what they do, and Apple is not going to create a situation in which an external group can determine how or if they can be sued in court based on how overreaching they feel that day.
Also go check how many arbitration clauses exist in your ToS, just as an exercise. I'm all for banning arbitration clauses and allowing consumers recourse in actual courts. I don't believe we should have companies sign their death sentence prior to doing business, this raises the barrier to entry and results in even less competitors who have to do the same.
If they start claiming they do that then I'll get angry about that too. You'll notice that only the fringe is accusing Apple of being liars or acting in bad faith here. Apple are pretty up front about what they do.
The problem with this plan is they're claiming they are only going to do selective law enforcement (only 1 US law, only things that are strongly supported by consensus and even then only sometimes). That isn't a position with a reasonable foundation, they are going to change their mind. I want them to change it in the "we don't snoop on people's phones" direction rather than open season.