End-of-life: The Pixels 4 XL, 4, 3a XL, 3a, 3 XL, 3 are no longer being updated by Google, so the CalyxOS releases for these devices only contain the fixes to the open source components, such as the OS code and the Linux kernel. Proprietary components such as the bootloader, modem firmware, and other firmware no longer get updates.
RE: Custom ROMS:
CalyxOS still supports the Pixel 3, with the following Caveats:
https://calyxos.org/install/
GrapheneOS would probably work too! :)