DivestOS is the next best thing to GrapheneOS. The founder, Tad, has contributed a massive amount to privacy on android, I've used it for a few years. It's based on LineageOS and has similar device support..
They are indeed different projects. GrapheneOS is maximum security possible. DivestOS is best effort security of old/EOL devices to prevent them from being completely e-waste.
> so one is limited to generally the apps
It has the only unprivileged microG implementation, please read this: https://divestos.org/pages/faq#appCompatibility