It is, but limited to the (excellent) Google Pixel devices.

I tried CalyxOS before GrapheneOS, a few years ago... I can't speak to CalyxOS now, but at the time, it seemed to be mostly just a hodgepodge of "this is a 'privacy' app; throw it in" without much coherence or polish beyond that.

Then I tried GrapheneOS, which was driven by Daniel Micay, who seems a hardcore security-minded person. GrapheneOS seemed to be working beating AOSP internals into better security shape, and very slowly tackling the apps. So, with GrapheneOS, it seemed I was starting with as clean and trustworthy an Android as one can get (to the extend Android can ever be clean or trustworthy), and in the interim I could add missing open source apps to my install. (Email, maps, SSH, chat, etc.)

GrapheneOS isn't the ideal I could imagine, but it exists, and I feel less violated by GrapheneOS than by other phone in the last ~15 years or so.

I have been running CalyxOS on a Pixel 6a for 6 months and I'm very happy with it. It does everything I need and found no big annoyances so far. A minor issue is MyFitnessPal not reading barcodes but that's it.