You're kidding, right? I was hoping after so many years it's clear. GDPR is about personal information. First, if you have no way of linking the IP to personal information, it does not apply. Second, even if it's linked (as in a web store etc.), storing it is perfectly fine! You just need to clearly state what information you store and for how long.
Everybody, also in the EU, are storing IP addresses. Everybody. Even the company who bragged they don't store logs for privacy reasons was caught storing them. It is important, it is necessary, and in many cases required by law.
Why risk getting entangled in weird foreign laws that might still have consequences here? The simplest solution is the best, just say no thanks in a simple redirect.
I understand why some people might be afraid of the risk. My point is that since you already implemented the code to detect EU customers, you could as well decide to not to set cookies rather than block them. In terms of complexity it's basically the same, but you get the benefit of increased exposure.
Everybody, also in the EU, are storing IP addresses. Everybody. Even the company who bragged they don't store logs for privacy reasons was caught storing them. It is important, it is necessary, and in many cases required by law.