Earlier quoted context omitted.
Apple's identifier can't be turned off; you can manually change it as often as you like, but it involves enough clicks that I bet few people do.
It can be turned off (although I think under the hood they just send zeros). But it’s on by default. https://blog.gingerlime.com/2020/does-apple-care-about-your-... EDIT also https://support.apple.com/en-us/HT202074
As another comment mentioned, the only effective mechanism is to reset the identifier periodically. That's not a disable mechanism, though.