So FP3 is shipped with the /e/ or you need to install it manually?

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.