I just said iOS can be 10-15, correlated with anything else it can easily be 30. Download an app and visit their support site and that's likely enough to narrow you down.
The web provides:
time zone
language and locale (accept-language header too)
iOS version
screen size and pixel ratio
text size
dark/light mode
reduced motion
ad blocker extensions for safari
An app provides (without additional permissions):
IDFA advertising ID (unique and cross app)
IDFV (vendor ID)
AdAttributionKit (which apple does obscure somewhat)
Battery level, charging state, volume, headphones
Various appearance settings again (font, dark/light, reduced motion)
Just slightly more permission granted via prompt can get you:
System boot time and uptime
Disk space
Keyboard languages and extensions
File timestamps
Then additional individual permissions (which people agree to all the time for specific use cases)... at this level they can single you out easily:
location
contacts
bluetooth
motion sensors
To Apple's credit they're trying to make fingerprinting more difficult and attempt to ban it entirely, but it's not at all impossible.