I use flat case most of the time, but I also try to stick to single word files so there is no case to get in the way.
I think for documents I might share like a PDF I’d use Pascal case.
In a classroom or teaching setting I will sometimes use Kebab case as I find it is the least confusing and makes it extra clear where the word division is. Similarly I avoid Dot notation since it’s confusing for folks coming from a Windows world.
And I would avoid Screaming because that’s just too loud anywhere.