> The second approach is to just write to the terminal like any CLI program, appending content to the scrollback buffer

This is how I prototyped all of mine. Console.Write[Line].

I am currently polishing up one of the prototypes with WinForms (.NET10) & WebView2. Building something that looks like a WhatsApp conversation in basic winforms is a lot of work. This takes about 60 seconds in a web view.

I am not too concerned about cross platform because a vast majority of my users will be on windows when they'd want to use this tool.