- Edited
Rooting GrapheneOS is inadvisable for a number of reasons, as far as security is concerned. It severely weakens the security model and exposes a massive privilege escalation risk for apps, and also means that Verified Boot would have to be disabled: In such a case, you cannot verify that OS you're booting cannot be guaranteed to be maliciously tampered with or corrupted. This removes a large pillar that the security model stands on.
There's no official method for rooting GrapheneOS, nor will there ever be one. As a project focused on retaining a strong base security model and further improving it, it would not make sense to.
You are free to build your own fork of GrapheneOS with root enabled, but at that point it is not GrapheneOS.