2wnin you can try using ADB, but I don't think you can see everything that's there.
If you suspect a compromise that persists after a factory reset, then you can flash GrapheneOS again then make sure your bootloader is locked, verify the installation, and then set up Auditor. I'd suggest using remote verification so you can be notified if Auditor detects anything.
If you installed GrapheneOS and completed the installation by locking the bootloader, etc. then it's unlikely that this has happened, but if you've already performed factory resets then there's no point in not flashing again even if it does nothing but put your mind at ease, just my opinion.