Great what they are doing - yet I found Shiftphone to be also fair, equally or better repairable and even more open for alternative Operating Systems. I think Fairphone supports 2 OSes officially, Shiftphone has a whole custom ROM list of ~10.
I'd be interested in the list, the website you've linked is super sparse (the full menu is like shop, some feel-good pages about device deposit and impact, blog, and contact us - no knowledge base, documentation, or somewhere where you'd expect to find OS info or even downloads)
And then in 2010, Maemo merged with Intel's Moblin to become MeeGo (featured on the Nokia N9). The MeegGo engineers who were let go (due to Nokia x Microsoft) then created Mer, and eventually started a new company called Jolla, who created SailfishOS based on Mer.
It's been 13 years already since SailfishOS was out, and if you include the Maemo heritage, it makes it the oldest surviving mobile Linux distribution.