https://grapheneos.org/features

CalyxOS is not a hardened OS. It greatly reduces security vs. AOSP via added attack surface, rolled back security and slow patches.

Compatibility with Android apps is also much different. GrapheneOS provides their sandboxed Google Play compatibility layer:

https://grapheneos.org/usage#sandboxed-google-play

Can run vast majority of Play Store apps on GrapheneOS, but not CalyxOS with the far more limited and less secure microG approach.

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://privsec.dev/posts/android/choosing-your-android-based-operating-system/ is an article with more long form comparisons between OSes.

GrapheneOS are the only ones developing a hardened OS. DivestOS is far more similar to GrapheneOS and uses some of their patches, but aims for broader device support by being based on LineageOS. DivestOS removed a lot of the mentions of GrapheneOS and even directly recommending it, due to the libel spread about GrapheneOS' developers. CalyxOS is putting users at risk by pretending to provide features it can't like it's firewall app which is just marketing fluff for the faulty LineageOS network toggles. It's on the same level as Freedom Phone. CalyxOS isn't similar at all and it's a misconception in the privacy-oriented Bitcoin and Monero community that they're making similar things. PureOS is just desktop Linux with a mobile UI. It comes along with all the issues of what it's based on.