> My understanding is that part of your IPv6 address is fixed from your MAC, so if I travel around with my laptop, Google could tell it is the same device connecting via IPv6 from anywhere in the world? Is that not the case?
That is not the case. Privacy addresses are used now to avoid the above situation.
A useful way of thinking about IPv6 addressing is that the /64 prefix used by autoconfiguration (SLAAC) is the basic unit of addressing rather than an individual IPv6 128 bit address. Every 3GPP smartphone connected using IPv6 gets a /64. This allows it to tether devices behind it. It also allows any IPv6 address in /64 be used so it can't be found by IP address range scanning because 64 bits is so vast.