As I read here (see i) the FP3 is now a target for /e/. /e/ (see ii) is a customized Android with focus on privacy, much more than LineageOS. /e/ is still in beta status, but already usable. Also /e/ follows the OpenSource philosophy much more than Fairphone.
Anyway, the developers of /e/ need information about already working roms on FP3 (see iii). Please post information there.
Help /e/ to make /e/ perhaps the first fully supported and actively developed google free custom rom.