I wrote a short blog post about this: https://www.uxwizz.com/blog/self-hosted-analytics-gdpr-frien...

This quote from the GDPR law is more relevant to your question:

> If the controller has the legal option to oblige the provider to hand over additional information which enable him to identify the user behind the IP address, this is also personal data. In addition, one must note that personal data need not be objective.