Not really.
iOS in lockdown mode has multiple features disabled (or crippled, depending on how you look at it), while GrapheneOS is just..... secure by design with secure defaults.
https://support.apple.com/en-us/105120
In iPhone also you cannot just turn on/off/adjust these protections one by one, it's all or nothing.
> OS in lockdown mode has multiple features disabled [...] while GrapheneOS is just...
...disabling features. Android Auto, Google Pay, enhanced GPS, SafetyNet, push notifications, support for any apps requiring device integrity, etc.
They aren't redesigning and re-implementing these features securely, they are reducing attack surface just like lockdown mode.