Sorry, it may not seem fair considering the topic, but certain OSes just aren't going to be listed here. GrapheneOS has a good reputation for doing well at what it does, but there are other OSes that some say are on a similar level as GrapheneOS in terms of privacy and/or security, but they're objectively not.
There's a lot of misinformation out there about these other OSes. We try to keep information on this forum accurate. Suggestions or discussion of insecure OSes on this forum may end up confusing people who don't know better, whether intentional or not.
If you are curious about other OSes and how they compare, I'd suggest taking a look at this comparison chart https://eylenburg.github.io/android_comparison.htm. For further information, you can try searching this forum. People with access to the project accounts are especially knowledgable, so you can see if you can find what they say about these other OSes here on the forum or elsewhere (official social media accounts are listed at the bottom of the contacting the project section on the website).