AFAIK, it's not illegal (per GDPR) to process EU citizen data in data controllers if the individual is no longer in the EU.
_Edit_: Yes, I read the article. It looks like this person got this email notification because they had activity in London (per their resume on their website). That doesn't make the email illegal nor does it mean their activity in Italy is going to be on a non-EU controller.
The email implicitly states that it's for the UK only.
However, I still don't think there's nothing illegal here. AFAIK & IANAL, It's not illegal to process EU resident data in data controllers outside of the EU (in the US).
However, the article still kinda vague to me, cause I got the same email, and I'm mos def in the US.
I'm so deeply inside the US that I have no idea how to check where google stores my data, and I don't really care cause the US has some bigger orange fish to fry. And pie to bake. Ajit Pie!!
It says on your website that you worked in London.
This email is likely a courtesy notification because you had activity in the UK, a UK billing address, or something that put you there, meaning if you have activity there again, the controller will be different.
What this email does not mean is that your Italy based activity is going to a different controller, so how exactly is this illegal?
* Read literally, the email only talks about the UK, not Italy.
* If you go to the UK again, then your activity in the UK will be on a nom-GDPR handler.
There is nothing illegal here, and just because you're sitting in Italy at this moment doesn't mean Google is moving Italian activity handlers. The email is a notification about Uk only.