Coincidentally I'm working on my own TUI framework for my book [1], so it's always interesting to see how other people approach it. I wouldn't, for example, use windows and drop-downs in the terminal; I think there are better approaches. Some of the most interesting text-focused UI experiments are taking place in Emacs and Vim, so that's where I'm taking inspiration from.
My framework is demonstrating the capability-passing approach to effects, which is the underlying architecture in most modern JS frameworks, Jetpack Compose, and "immediate mode" toolkits (though the authors are not necessarily aware of capability-passing as a concept). If you've read recent posts on "algebraic effects" or "effect handlers" it's in the same space. It makes for a quite pleasant user experience. I'm enjoying the work uniting theory and practice; one of the benefits of writing the book is I can justify these excursions.