It's well-supported by LineageOS and will probably remain supported for longer than most other phones. That's the only benefit that I'm aware of, but that makes it already better than like 99% of phones on the market.

No privacy nightmare ui (like miui) and no bloat or privacy invasive apps (no Facebook preinstalled and suchlike). And if you ever want to switch to a degoogled phone using microg it will be easy (a degoogled phone means of course Google will not be able to spy on your notifications, locations, apps, etc.). You can try to check /e/ system phones, or iodè phones too (both degoogles), but you really need to know what you're doing and which of the apps you use will not work (those are rare, but exist)

You can say that for absolutely any phone/device in existence. As for Graphene, I've ran tcpdump on my router for a week against the device's IP and confirmed that it only talks to the documented default connections on their site.

It's not an easy solution. GrapheneOS is really good, but you need to be sure you will not need Google service and NEITHER MicroG, because those aren't supported by GrapheneOS

what do you recommend then?

Privacy can be controlled on application level, but there are a lot of system stuff that user can't change and the best solution for system is GrapheneOS in terms of security, as I said in first comment.

Google is evil, no question about that, but Google is just a brand / label on the phone. Ironically, but most secure and privacy-friendly phone is Google Pixel without Google

As for privacy, any phone capable of running lineageos is fine, but lacks security