Author here! Aside from Terminal.Gui, most of my GUI experience comes from SwiftUI on iOS and Mac. However, C# also has another cool terminal library called Sadconsole (https://sadconsole.com/) which I've used in the past to work on a Roguelike(https://markjames.dev/2020-05-21-making-a-roguelike-in-c-wit...). According to the developer, "SadConsole is an MonoGame 3.7-based game library that provides an engine to emulate old-school console and command prompt style graphics. One or more textures are used to represent the standard ascii character set. SadConsole allows you to create console instances which can be managed independently of each other. A console is made up of individual cells which can have a foreground, background, character, and a special effect applied to it."
Free Pascal comes with Free Vision, a fork of Turbo Vision. I suspect it's still the fanciest TUI library around in terms of what you get out of the box - FP's own text-mode IDE is written using that library.
Turbo Vision was also ported to modern C++, although I'm not sure what the quality of those ports is.