This would be the hardware keys for all iCloud data. With the Secure Enclave the keys never leave the device.
Discussion
But I’ve never heard of an iPhone’s Secure Enclave being compared to cold storage, because an iPhone is always connected to the internet, therefor not cold I guess 🥶
Yes I would agree with you that it is not a cold wallet, meant to say it is a similar concept when storing secure data like keys.