Today Facebook Messenger sent me a second notification about a message because I hadn't responded to the first one 6 hours earlier. They are hell-bent on making the experience as miserable as possible to drive engagement.

The rule about promotional push notifications being opt-in still exists in the App Review Guidelines, it may just take some public shaming to get Apple to enforce it.

(While many apps from big publishers skirt the rule, DoorDash is the most egregious I've noticed: if you opt out of promo notifications, they'll try to trick you into turning them back on every time you place an order, suggesting that you won't receive delivery updates otherwise.)