I fail to see the relation to Turbo Vision.

Fair.

Notcurses' principal author aspires for it to provide a widget toolkit for TUIs[1], but much of the demo and much of the commit log to date is heavily focused on graphical capabilities and lower-level details.

It may be that one day it ships with a robust widget toolkit; or perhaps someone else will build another library on top of notcurses with that as the principal focus.

I'm also impressed with the effort put into FinalCut[2], but notcurses seems to me to be paving a more interesting path forward for TUI development.

[1] https://nick-black.com/htp-notcurses.pdf, see e.g. page 3

[2] https://github.com/gansm/finalcut