Assuming that you're using a modern IDE: it is an order of magnitude quicker to model the domain (classes + attributes) in code and project them as diagrams, say with graphvis.
High level boxes are great for thinking about systems but the key there is abstraction - minimal viable level of detail..
Dont you want to discuss and talk about a design before you even touch a keyboard? In my projects we always discus high level overviews with pen and whiteboards. Nobody should even dare to touch a keyboard.
Absolutely, I pretty much always start with design sessions on a whiteboard (or if remote a call using draw.io).
That discussion is almost never going down the the level of an individual class and NEVER adheres to the UML standard.
Very occasionally I've had discussions about class structure by drawing class name + methods on a whiteboard but having the same discussion using Visual Studio's UML projection was just as effective.
this phrase caught my eye, "minimally viable level of detail", to which I immediately thought "minimal detail for a coherent thought". That's a cool concept actually I might hold on to and develop.
If you're creating diagrams with graphvis, you're just coding on another language. The benefits of diagrams appear when you draw them by hand (or graphically by mouse).
I generate them: initially with my own generator (which is copyright an employer from > 15 years ago), on a later project I found that Doxygen can do do that for you out of the box :-)
For interactive discussion I just use Visual Studio's projection, for databases I use the SQL Server Management Tool ERD projector or pgAdmin if I'm using Postgres.
High level boxes are great for thinking about systems but the key there is abstraction - minimal viable level of detail..