No they can't: the whole point of RFC4941/8981 is to prevent that. The source address for external connections is effectively randomized.
All that can be inferred is that it came from your network, but even with NAT you know that anyway.
It's still unique to one device right?, even if random my argument still holds.
Or do you mean to say multiple devices can use the same address?
note: I've read the RFCs and they just mean - initial address is random but unique to a device. Each day the address will likely change but new address is still unique to the device (otherwise how would routing work).
This is what I structured my inital argument on. Do you see any fallacy in logic?
If you set up your device to spin up a new IPv6 address every hour (or even every minute), how will they track you using IPs?
On macOS it's 24h, but it doesn't have to be:
$ sysctl -a | grep temppltime
net.inet6.ip6.temppltime: 86400Minutes or less I guess would defeat tracking, but then what's the point?, it's almost equivalent to NAT it still breaks reverse connectivity? and does it actually work?
It also feels like a workaround for an oversight.
But how would they know it is to the same node?
I have my DSL router-modem reboot every night, and I get all sorts of crazy results for ads: I'm in southern Ontario, as is my ISP, but they service folks in Quebec, and so sometimes I get Youtube ads in French since (per my IP) I'm "in" Quebec.
Similarly with the reboot I get a new /64 prefix delegation (actually /56), so I would hazard to guess if IPv6 starts getting tracked, I'd get the same crazy results.
No one cares about tracking by port. Folks are tracking by IP(v4) address.
I know this first hand because I have my DSL router-modem auto-reboot every night (built-in Asus functionality), and I get all sorts of crazy results for ads: I'm in southern Ontario, as is my ISP, but they service folks in Quebec, and so sometimes I get Youtube ads in French since (per my IP) I'm "in" Quebec.
And given that I have IPv6, most OSes generally use that as a first preference for connectivity, and so my IPv6 address/prefix is "in" Quebec.
And this is even with cookies enabled, which should make tracking by browsing easier (esp. since I get decently-accurate recommendations based on viewing history), but yet I still get French ads because my IPv4/IPv6 address is "in" Quebec.
So I have no idea what people are talking about when they say IPv6 will make tracking easier than IPv4. With RFC 4941 it's a solved problem IMHO and no worse under dual-stack than it is under single-stack.