Identifiability for IP addresses uses an even lower standard. The GDPR says that for something to be truly anonymous, there must not be any “reasonably likely” means for identification, even with the help of third parties, even when relying on additional information. There has of course been litigation about this, in the form of the Breyer v Bundesrepublik Deutschland case. It was based on the GDPR's predecessor law, but it used virtually identical phrasing so the conclusion still holds.

The European Court of Justice constructed a hypothetical scenario to show that identification can reasonably be likely. Let's say the website was attacked by a hacker. In a logfile, you find the attacker's IP address and want to prosecute them. So you report the incident to whatever authority is responsible for such incidents, which then gets a court order so that the attacker's ISP discloses information about the IP address. As long as the ISP knows to whom that IP was allocated at the time, there is now a reasonably likely chain of events that leads to identification of the person behind the IP address.

In this case about Google Fonts, the court says that it's sufficient if the website operator or Google have the “abstract means” for identification, not whether they actually did this for this plaintiff's specific IP address.

A solution would be if the EU forbids ISPs from keeping such logs, but given repeated attempts at mass data retention laws for national security purposes and pressure from the IP industry^W^W film and music industry for copyright infringement prosecution purposes, that doesn't seem likely.