Currently i stumpled cross the same problem
But good to know, that i'm not alone.
I will try, if the achievement is cross profile.
edit: Okay, tried. No, visiting the missing city with a no-mods profile does not help. So i will leave the achievement, till the mod is changed. No interrest in trying, what happens wih my employees and their current deliveries, if i disabled promods and stuff ^^
edit 2023-04-11: Really sturdy game
I tested around. Disabled all my mods. One garage was not in a base city, but trucks, drivers still are there.
Drove to the missing city, got the steam achievement, logged out, reactivated all mods and loaded the state with the missing, but travelled city again.
Even the info driven roads in the mod areas are again correctly marked. The data in the save games/cloud data must be interesting.
PS: Read in the end, the edit of the moderation. Sorry, will not happen again.