Modern advanced lockers (SCS SigMaker) actually cryptographically sign files. The basic unlockers do not work on these. Most "locked mods" you find on public forums are the older ZIP-password type, which the unlocker handles perfectly.
The is the solution you’ve been looking for! It allows you to decrypt locked .scs archives so you can edit definitions, update models, or fix outdated mods for the current game version. SCS Unlocker for Locked Mods - Euro Truck Simulator 2