I'm not going to pretend like I'm an expert but I played like 20 hours of car mechanic simulator and was able to help my buddy with pointing out some weird things when he popped the hood of his car.
And I also wonder if a few hundred hours of Truck Simulator will give me some novice level experience in truck driving.
As someone who worked for a trucking company before, I can tell you that no amount of simulation will equip you with the horrors that truck drivers have to live through every day.
I've crashed my trailer dozens of times in the Euro Truck Simulator and may have committed a bit of "floor it because not a crime if they can't catch me".
I mean you can probably back up the trailers fine, but all the "stuff" involved with hooking up and unhooking is completely omitted from ATS and ETS/ETS2.
Shifting gears is another thing, I can shift a 6 speed, but if you put me behind a real 18 speed with splitter and range gearboxes, I guarantee I'd be grinding the shit out of those gears, over-rev or lug the engine... Etc.
The popular truck "sims" are not sims, they are basically one step above arcade games. And I say this as someone who likes playing them. They are fun, but they are not sims.