LineageOS

LineageOS picked up directly where CyanogenMod left off in 2016 after that project shut down, and has since become the de facto foundation of the custom-ROM ecosystem -- GrapheneOS, CalyxOS, /e/OS, and many others all build on top of LineageOS's own codebase rather than starting from bare AOSP. It aims for a clean, close-to-stock Android experience with a moderate set of useful additions (a more capable audio equalizer, extra customization options, its own privacy guard for permission management) rather than heavy theming. Its device support list, maintained by a large distributed community of device-specific maintainers, is the widest of any custom ROM, though official support for any given phone depends entirely on a volunteer maintainer picking it up and staying active.