MAC

MAC#

Media Access Control

12 digits (0-F i.e. 16 possible chars)
12 hex digits
6 bytes
46 bits
16^12=2.81E14
281 trillion
281, 474, 980, 000, 000
two hundred and eighty-one trillion, four hundred and seventy-four billion, nine hundred and eighty million
40k MAC per person on earth

Organization Unique Identifier

Or are there any (maybe cloned?) network interface cards that have the same MAC address as another NIC?

What is the probability of having two identical MAC addresses within one network?

The hardware identification addresses that the IEEE distributes are unique. That makes the probability of matching MAC addresses zero.
On the other hand, some hardware MAC addresses are programmable, which makes them spoofable. This means that it is possible for two machines in the same network to have the same MAC address.

Apple release with iOS 8 in 2014
Android followed the same and introduced with android 8, in 2017; made it default ON with android 10+
Earlier it was used for probing purpose, later adapted it for association as well
Random MAC could be identified by looking at the 2nd digit of the MAC, it should be 2, 6, a, e
Affects N/W vendors and service providers

Ref:

https://www.mist.com/get-to-know-mac-address-randomization-in-2020/
https://securityaffairs.co/wordpress/57076/uncategorized/mac-address-randomization-flaws.html
https://hsc.com/Resources/Blog/Effect-of-Apples-MAC-Randomization-Feature-on-Enterprises
https://globalreachtech.com/blog-mac-randomisation-apple/