I just started my first game in B18 and the colonist bar no longer shows who is idle. Is this a game thing or is one of my mod doing this?
Probably a mod. My colonist bar is fine.
If you just started, there's a minimum time that has to pass before the "idle workers" alert pops up. It should appear after the first in-game day or so of the colony's life.
It is definitiv a mod, the colonist bar don't show this kind of information on vanila gameplay.