It didn't come installed and the FP3 isn't sold anymore so you'll have to install it. It was dead easy though, not anywhere near the complexity of installing Lineage back in the days (though that's gotten easier too).
/e/ on FP3 has been my daily driver for 1.5 years and my daughters run it on their FP4s with no problems at all.
Murena have been selling Fairphones preinstalled with /e/ OS. I think right now its the FP6 and FP5 they do.
https://murena.com
Its not only Fairphones. I'd say they've got an interesting mix of tech there. I think they even sold refurbished pixels flashed with /e/ for a while.
It didn't come installed and the FP3 isn't sold anymore so you'll have to install it. It was dead easy though, not anywhere near the complexity of installing Lineage back in the days (though that's gotten easier too).
/e/ on FP3 has been my daily driver for 1.5 years and my daughters run it on their FP4s with no problems at all.