That’s not the issue. You can attempt as many passwords as you want in actually secure password managers as well. KeepassXC for instance IS secure, you can still brute force the password, but because of the hashing algorithm they use it’s extremely hard. With PKZIP if you know some of the words in the file, you can easily guess the password in just a few hours because the encryption algorithm it uses isn’t secure
wouldn’t it have been easier to just read the source code? (not that GNU’s code is easy to read, but still)