Check that your root folder contains AssettoCorsa.exe and the changelog.txt reflecting version 1.16.4.
Download the full digital installer package through an authorized platform such as the Steam Assetto Corsa Store Page . assetto corsa v1.16.4 download
For many in the community, the game was in a "golden state" during this version. It was stable, the physics were refined, and it was just before the introduction of some of the later networking changes that altered how online multiplayer mods functioned. Check that your root folder contains AssettoCorsa