Also you do not seem to understand that bugs and resulting security problems are something that happen every day - and get fixed quickly, usually, after discovery. This is what they mean when domain experts say things like "security is a process".
Also here we see a perfect example of why you want to use open source software for all governmental software: after a bug was found your admins can see the code changes and understand, if the bug still exists or not. Even more, only with open source software your admins and developers can read the code and search for bugs, too! This is what makes open source software a very good idea!
You are welcome to the world of free and open software, and after some reading about the basic principles I am sure you will understand why open source software is used by so many companies and organizations around the world.
BTW re the website you pointed to: I see a very annoying, totally absurd cookie dialog that makes me click at least five times and still does not give me a choice to not accept cookies at all. Please do not link to that website until they wake up and stop insulting visitors with this UI nightmare and learned that nobody needs to set cookies to publish content. Also this is not a website a pro developer would ever read or point to - always prefer to point to the primary source of information.