There are other options like
Calyx. It's questionable at the moment, as there is some question about the signing keys and the developer who controls them. I'd probably avoid that one.
Lineage of another option. Depending on your hardware there may be builds. These are made by host of developers, so dyor and see what the state is for your hardware.
I've been using custom Android builds for over a decade. I've used lineage in the past. It was good on some hardware, but had incomplete support on others. FWIW graphene is the most polished of them I have used. I currently run it on a pixel 6a as a secure secondary phone.
It seems counter intuitive that a phone from Google would be the best choice. However security researchers and privacy experts pretty much exclusively recommend it. @Final is part of the GrapheneOS team, and can explain it better than I. But basically the pixels are the only hardware that have the features necessary for graphene to do what it does.
A letter to the CalyxOS community
A letter to the CalyxOS community
LineageOS – LineageOS Android Distribution
LineageOS Android Distribution