I'm going to suggest that it's on the universities to find a way around that problem. It's a real problem, but everything being publicly available online is how the world is now. Just varying assignments every year should be enough. If reasonable variations don't make the assignments challenging enough? Well the students are always going to be able to find some reasonable variation online. Starting from absolute scratch is just not a thing anymore in most fields.

It should be on a student to choose whether or not do they want a challenge, what particular aspect and what degree they'd like to be challenged in. The job of an educational institution is to educate, whoever interested can easily invent a challenge for themselves or use an old challenge without looking at ready solutions if they so desire. Forced artificial challenge policy is questionable.

They have found a way around that problem...they expel students who share solutions.