The IP address does not give personal details, the nearest to personal details is that it gives the area or city, such as Manchester, England, UK.
If there is a single computer on that IP, then it is the IP address linked to the computer. If the computer is connected to a router, then it is the IP address of the router. There is no such thing as an Internet directory giving namer and addresses. It is not like the landline phone system with a phone directory or you could call an operator and try to match a name and street address to a telephone number. If you are using a public WiFi connection, in a cafe for example, then it is the IP of the wireless Router
So there is no GDPR concern over over jD storiing the IP address. If you want to see what your IP reveals then try a site likehttps://whatismyipaddress.com/
The next release of Joomla (3.9) is aimed at GDPR so I suggest you check out that firsthttps://www.joomla.org/announcements/release-news/5731-joomla-3-9-and-joomla-3-10.html