Are both of them ula addresses? (both of them starting with 2). If they are not the same then the ISP is providing an internal unique address for isp internal configurations.

If so, are they having the same network? ( The first 48 bits) if not, then is probably a miss configuration but probably in their side. But with no practical effects. You could ignore it.

If yes again, then it is a miss configuration and it shouldn’t happen, but this time it could be in your side, check that the dhcpv6 daemon doesn’t try to give an ipv6 address To your Wan port

Even if you have a valid point, modern fingerprinting technics usually is done through your data and the connection dependencies of them (which accounts are activated from the sane computer and so on).

Selfhosting remove some links between your data set like the files you store in drive, the people who appear in your photos, your contact list, to whom you email… Etc etc

Suddenly all this data is vanishing from the big techs, so, in theory it would be possible to make that association process more difficult

Then follow that path, once you are comfortable with the approach you can start hosting more and more services,to the point that you can selfhost your own messenger services or ms teams services.

Once you are in that situation, you can think in accounts rotation and/or burner identities to address the services you can not pull from the big techs

You need to start reducing your fingerprint on internet.

The only reliable way to do so is selfhosting your stuff.

There are a few communities here in lemmy, so check on them