So, I tried to add a car without changing it, and everything went OK until I accelerated the automobile, at which point the game abruptly halted. Details: No ability to alter the radio, no engine sound.

https://192-168-100-1.id/

You should not have access to mod vehicles with a demo account in first place.

Quote from Katakuri2003 :

So, I tried to add a car without changing it, and everything went OK until I accelerated the automobile, at which point the game abruptly halted. Details: No ability to alter the radio, no engine sound.

you should stop modding demo lfs instead buy s3 and then start modding in lfs-editor