As an example I think Androids have a single device ID which is given to all apps. But iOS has a per app device ID.
The marketing department exploded when Apple announced that change, it made user conversion tracking completely useless.
And of course there are guidelines that disallow most of the abuse scenarios I suspect people want to imagine: https://developer.android.com/identity/user-data-ids
The main difference is it's opt in on iOS, but opt out on Android I believe.
On iOS, when the app pops up and asks to track, if the user says no, the app can't access the system advertising ID at all, and also is not permitted to track activity via other means like email address, user ID, etc (but the only thing that's technologically enforced is the system advertising ID, it's only forbidden by policy to not use other tracking methods).
Given the huge fit Meta threw after Apple implemented this, while they were silent about Android, I'm inclined to believe Apple's method has more of a privacy impact.
Also worth noting Google is hoping to move away from device-level advertising IDs with their "privacy sandbox" thing.