Apple tries as much as possible to stick to as few different products and components as possible, to maximize economies of scale. For example, the company has chosen to release new cheaper products with the same processor as in older ones, such as the Iphone SE with A13 processor.
Last fall, the company made an unusual change to one of its processor designs, reports 9 to 5 Mac. We do not know of any previous occasion when a certain processor design has changed while it continues to be manufactured.
It is about the security circuit Secure Enclave which, among other things, handles encryption and boot security in iOS gadgets (and now Macs with Apple Silicon). In a support document Apple writes that the built-in storage in Secure Enclave has been upgraded to the second generation of new products released in the fall of 2020 with the processors A12, A13, S4 and S5.
No new gadgets with A13 or S4 have been released, but Homepod Mini and Apple Watch SE have S5 processor and eighth generation Ipad has A12 processor. These thus have increased security compared to older products with the same chip, such as the Iphone XR with A12 processor.
The difference between the first and second generation of security storage is that the latter adds a new, more secure way of storing some of the data required to unlock saved passwords.