IP addresses are quite static. Most phones and laptops come "home" once a day and get attached to the home IP. Do it for long enough and you can household all the other IP v6s, MACs etc. that are untethered.
MAC addresses don't leave the local network, so it's not relevant to web tracking. Moreover it's randomized by default on ios/android so the tracking potential is limited.
MACs are always randomized, even when connecting to the same network. At least as far as modern devices go.
Am I wrong?
I've had the same prefix for five years now.
And yeah, sure, my device cycles through ephemeral IPv6 addresses often, but always within the same prefix.
Group IPs somewhere between /64s and /56 and you'll essentially get a household identity, at least for a few days to a few years.
Proper randomization can be enabled through the developer settings.
https://source.android.com/docs/core/connect/wifi-mac-random...