The fact that Keychain isn't in this list of APIs despite also being available to all apps by a developer (and optionally synced via iCloud) also points to them being OK with shared logins between apps (or they just forgot???)
It seems like they forgot the actual API that allows tracking users across installs, lol
I dont think the keychain can be used to track...
Just to the same or slightly higher extent as UserDefaults which is on this list
Fingerprinting is more of an intent. Google will absolutely tell you it's just to ensure consistency among their products. Their most important product being targeted advertising. Using it to enable consistent targeted advertising would be what the advertising industry calls fingerprinting.