According to variation theory in learning, variation is important in the learning process because it develops different ways of seeing. It allows people to learn to do something in a certain situation, and then, due to the perceived differences and similarities between situations to do something completely different in another situation.
In this sense, when preparing learners for future problems that are known to us, it is important that in the training course, they practice with problems that are similar to the future ones.
But when our objective is to prepare them for unknown problems, then the best way to do this is by allowing them to deal with as many different kinds of problems as possible. The less you know about the nature of the future problems, the more varied the problems should be. This experience of variation will enable your participants to transfer and use the knowledge and skills acquired in a completely new situation in a completely new way.