GrapheneOS wants to make a FOSS Android with the security model that makes it hard for any bad party to break into the phone.
LineageOS wants to make a FOSS Android that respects user's privacy first and foremost - it implements security as best as it can but the level of security protections differs on different supported devices.
Good news is that if you have a boot passphrase, it's security is somewhat close to GrapheneOS - differing in that third parties with local access to the device can still brute-force their access whereas with GrapheneOS they can't - unless they have access to hardware level attacks.
GrapheneOS wants to make a FOSS Android with the security model that makes it hard for any bad party to break into the phone.
LineageOS wants to make a FOSS Android that respects user's privacy first and foremost - it implements security as best as it can but the level of security protections differs on different supported devices.
Good news is that if you have a boot passphrase, it's security is somewhat close to GrapheneOS - differing in that third parties with local access to the device can still brute-force their access whereas with GrapheneOS they can't - unless they have access to hardware level attacks.