When I look at my car list, I'm not able to sort them by mod. I think you may be referring to the 'drive' portion of the game when choosing a car. I'm referring to the 'content > cars' portion where we can see more details and even delete the cars from the manager.
This is Content Manager
Content Manager — A brand new alternative launcher for Assetto Corsa. Consist a complete list of standard launcher features, plus huge extended functionality with advanced ability speed and usability.