In the European privacy framework, and legal framework at large, you can't terms of service away requirements set by the law. If the law requires you to keep the logs, there is nothing you can get the user to sign off on to get you out of it.
OpenAI keeping the logs is the "you have no privacy" part. Anyone who inspects those logs can see what the users were doing. But now everyone knows they're keeping logs and they can't lie their way out of it. So, for your own legal safety, put it in your TOS. Then every user should know they can't use your service if they want privacy.