No, Murena sells devices with /e/OS which is fork of LineageOS which drastically rolls back privacy and security compared to it. LineageOS itself rolls those back compared to the Android Open Source Project but not nearly as much as /e/OS. LineageOS would be a better choice for privacy, security, app compatibility and usability than Purism's product.
GrapheneOS and /e/OS are very different operating systems. GrapheneOS is a hardened OS with massive privacy/security improvements and a far different appropach to mainstream app compatibility. GrapheneOS can be purchased preloaded on devices including from companies like NitroKey, so that is not something that's a difference between them. GrapheneOS is based on AOSP directly, not LineageOS.
https://eylenburg.github.io/android_comparison.htm is a third party comparison between different alternate mobile operating systems. It could include many more privacy/security features but it's a good starting point.
https://grapheneos.org/features provides an overview of what GrapheneOS provides. It doesn't cover all of the features but it covers a lot of them.
/e/OS lags very far behind on shipping Android privacy/security backports, lags a year or more behind on shipping standard privacy/security patches and does not keep the standard Android privacy/security model or features intact. Like LineageOS, /e/OS mainly supports devices without proper non-stock OS support and without firmware/driver patches. For the few devices they support which do provide those updates, they are much worse than LineageOS at shipping them to users. They don't use standard hardware-based security features even when they're made available to an alternate OS. /e/OS is not a safe option because going months or even years without critical browser engine and OS updates is a serious problem. It is not an academic or theoretical issue. They are failing to patch critical issues and some of those are known to be exploited in the wild.
You can run nearly all Play Store apps on GrapheneOS, but not /e/OS with the much more limited and less secure microG approach. https://bsky.app/profile/grapheneos.org/post/3lamcjfv5r22s explains the difference in approach. Of course, their approach certainly provides dramatically more mobile app compatibility than using the desktop Linux stack on mobile as is being proposed in the original post.
Easy