GrapheneOS isn't rooted. PayPal works on GrapheneOS and doesn't try to ban using it. However, they recently shipped incorrect anti-tampering code incompatible with our secure app spawning feature (exec-based app process spawning). It can be worked around by disabling the per-app secure spawning toggle for PayPal. For simplicity, there's a per-app exploit protection compatibility mode toggle which sets all the finer grained exploit protection toggles to the compatibility mode.

GrapheneOS is an operating system rather than read-only memory firmware. There's a ROM in early boot (boot ROM) which loads the SoC boot firmware from the SSD which loads other SoC firmware from the SSD and then loads the OS from the SSD.