Is it possible to ensure that only one document can be open at a time? My target is macOS 15. The idea would be that the user is alerted and no existing document can be opened (e.g. drag and drop, file->new, Finder etc).

I started 100 Days of SwiftUI last year but then stopped a few projects in when life got busy. I've been shaking off the rust and preventing it building up in the future by making flashcards with Keynote/Goodnotes to study, but I'm starting to reach days where the checkpoints are too long for a single flashcard and the longer projects I've written need to be their own worksheets if I want to make review material for them.

I'm definitely going to put simple facts on flashcards, like true/false stuff, common misconceptions, small code examples, etc. But should individual functions and properties that I'm introduced to get their own flashcards, like animations I add to projects? Or would that be overkill?