Some modders hard-code the "obsolete" check into the car's data.acd file. You can force the game to ignore this.
When the error says "Assetto Corsa is obsolete," it is a poor translation of: "Your client files do not match the server's locked-in 2019 standard." In a world where most sim racers use Content Manager and hundreds of mods, being forced back to "vanilla v1163" feels like being told to drive a horse and cart on a Formula 1 circuit. assetto corsa is obsolete v1163 is required fix hot