It appears from my limited searching that Really Wireless is an interesting MVNO running off of T-Mobile's network and what appears to be some kind of service that seems like some sort of large mesh network. For a wireless company that claims to be privacy-conscious and to not know or support GrapheneOS is also interesting.
My first question would be if you are using their app and if you've run into any issues using it, as it seems like the app is required for eSIM setup from what I've read. Or is activating the eSIM in the app giving the issue?