I will be arriving at FCO at around 20:00 and wondering how to get to the city center (or close enough) to then get to my accommodation in Fiumicino.
This is not a question of FCO - Rome, but FCO - Fiumicino city!
Bus? Train? Uber? Bolt? Taxi? What are the options and their pros and cons?
Answering my own question: Right outside entrance 3 of the Terminal 3 of FCO there is a blue patch on the asphalt saying "Bus to Fiumicino City Center" [1], it's line 8 of the Trotta bus service, 1.5 Euro, runs every 30 mins (in the summer). Schedule here: https://www.trotta.it/active/linee_estive_fiumicino.aspx?m=1#undefined14
It doesn't stop in the center, but you can walk afterwards ... 10-15 minutes.
[1] Right in front of the entrance! DO NOT go where the shuttle busses (to Rome Termini) stop.