Wikipedia (https://en.wikipedia.org/wiki/List_of_open-source_mobile_pho...) lists /e/OS, CalyxOS, IodéOS, LineageOS, postmarketOS, Ubuntu Touch, the latter two being non-Android, the rest Android derivatives on Fairphone 5. Fairphone 6 has only /e/OS and IodéOS listed at the moment, but that will probably change after some time on the market.
There are also various reports of things like running e.g. Fedora on an FP6, https://www.notebookcheck.net/Fairphone-6-turns-into-a-Linux... or Debian on FP4/5, but those generally aren't something that is usable due to lacking support for basic things like calls.
There are also various reports of things like running e.g. Fedora on an FP6, https://www.notebookcheck.net/Fairphone-6-turns-into-a-Linux... or Debian on FP4/5, but those generally aren't something that is usable due to lacking support for basic things like calls.