I'm getting:
Error: Could not find or load main class DOS Trader.jar
Caused by: java.lang.ClassNotFoundException: DOS Trader.jar
I'm using the latest version of Java. I'm running Pop!_OS (It's an Ubuntu distro).
Ah, too bad. I think this game was made in Java 8, which has become a bit old at this time. You should be able to play this on Java 8, but maybe it's not really worth it to install that version on your pc.
Thanks for reporting this, but I'm afraid I'm not able to update this game anymore due to some technical issues.