I believe you're mistaken. GDPR allows you to record IP addresses for normal operation of a site, which specifically includes logging. No banner is required.
GDPR is not "vague" about this; perhaps you haven't read it (as laws go, it's pretty easy to read).
It's easy to read because it's vague, and it's going to allow some regulator to decide whether my use of IP addresses constitutes "normal operation." Puts a hell of a lot of trust in government officials to decide who is worthy of prosecution.
It reminds me of the war on drugs in a lot of ways.