> browsers could pass these preferences to all websites [...] Or use headers?
This is what Do Not Track was supposed to be, and the stalking & advertising industry didn't care.
To disable notifications requests, you can just disable notifications in your browser settings. For Chrome, go to Settings -> Site settings -> Notifications -> set to "Blocked".
> Maybe there is a way browsers could pass these preferences to all websites... something like standardized "omni-cookies" that apply across all domains? Or use headers?
You appear to be thinking that these websites care about what you want. They do not. They care about what they want you to do, and that is buy whatever they are selling, and they will use whatever technology and dark pattern is available to increase the likelihood of you buying.
It's not that they aren't aware that people don't want to be annoyed. They are. You don't need a new technology to tell them. They just don't care about what you want. Similarly, telemarketers aren't sitting in their conference rooms trying to figure out which citizens don't want to be cold-called and scammed into a contract.
You can solve this on an individual level: I don't care about cookies is a browser plugin that takes care of the cookie bars for you. Adblockers and Privacy-Plugins are great at blocking the domains of LiveChat-services and your browser lets you control your notification settings.