Is it possible to have multiple steps opened/being displayed on Angular Mat Stepper?
I can only show one, and I've been trying to look for an answer, but I didn't see anything about it.
It it not possible to show more than one step at the time. This is because, as explained by the documentation here, its intended use case is to provide a wizard-like workflow by dividing content into logical steps.
For your use case I will recommend you to use the Expansion Panel instead, as it is possible to show multiple expansions at the same time as shown in this example here.