A short quest that can be done after you complete the story in Petrichor, Nostoi Region. The quest is simple enough that you can complete it yourself after finding the location.
How to Start Latecoming Homecoming Quest in Genshin Impact
You can start this quest after completing the main quest chain (Canticles of Harmony) in the new area of version 4.6 and wait for a daily reset. Talk to ??? (lady NPC) near the Waverider Waypoint in the Nostoi Region.
Giulietta will request for you to bring her to Bayda Harbor in Sumeru. There, you will meet another NPC called Giustino who will ask you to bring him to Petrichor (Nostoi Region).
At Petrichor, when being told to find Giustino who ran off after arriving, talk to Giovanni and he will lead the way for you.
After that, you can keep following the quest navigation until the end because there are no puzzles here. You do need to fight a single Fatui Pyro Agent though. In the end, you will get the Slow Homecoming achievement.