This isn't fully open-source in contrast to something like Replicant: https://www.replicant.us/

LineageOS is also better, but includes proprietary drivers: https://lineageos.org/

Sailfish has proprietary drivers AND many of the GUI components are proprietary. I don't know if this list is still up-to-date: https://wiki.merproject.org/wiki/SailfishOSS