UID tracking on One platform but not the other

We have matomo tracking on both our iOS platform and Android platform. We can confirm we are not specifically setting the UID on either platforms. But the Android platform is tracking the UID while iOS is not.

Could there be a reason this could be occurring?
Does the Matomo library on the platforms track the UID by default?
Does the Android library only tracks the UID by default and the iOS library has to specifically set the UID?