My main source regarding the privacy/security stuff is this blog (in German). To be clear, /e/ isn’t bad on that front, the alternatives are just better.
You can read mode on the OpenAI integration in the /e/OS forums and the fairphone forums.
/e/OS is just another android rom, and unlike calyxOS or grapheneOS, /e/OS isn’t very privacy focused. There’s some weird stuff regarding a hidden “license id” and some of their services rely in openAI. You might as well just use a “real” privacy-first android rom if you’re trying to get away from tech giants, their tracking and closed source software.
CalyxOS development is paused right now but it’s still available and campatible with more devices. I wouldn’t recommend a currently unsupported OS but personally I’m still using it on my Pixel 7a. I had some google integration issues in GrapheneOS, plus I prefer the focus on privacy instead of security.