These are Steam Workshop items and not considered as local mod. They are not working in TMP, but working in single player.
The local mods lets you make the single-player modifications in TruckersMP (paintjobs, accessories, trailers etc.).
Local mods are only visible to you, other players cannot see.
You can find local mods in some Discord servers and websites but you must be careful when downloading these mods as some of them may have malware.