Is the line between TUIs and GUIs blurring?

I've heard a lot that a benefit for using terminal software over GUI apps is that they use much less resources. And that's why its better to SSH into servers rather than have them use up resources for a display server, Quartz X11 Wayland etc.. But terminals aren't just outputting raw text, they have text and background colors per character, TUI frameworks have been made for them to essentially have GUI-like elements, like Neovim and Ranger. Things like the [Kitty Graphics Protocol](https://sw.kovidgoyal.net/kitty/graphics-protocol/) seem to blur the lines. While I don't know the technical details (please explain if you can!), it's nice that it can render images in the terminal, but how is it different, especially the technical details and resource demand (CPU GPU RAM etc.) to display servers?! Does it work without a display server running on the client, like a "raw" linux terminal where the desktop environment isn't loaded?

I haven't look at this much either but there's also [kui.nvim](https://github.com/romgrk/kui.nvim), a terminal GUI framework built on-top of Kitty Graphics and it seems to escape the TUI constraint of only being able to visualize things with text characters, being able to draw elements of any length. There's a [comment](https://new.reddit.com/r/neovim/comments/110znd4/comment/j8f6pb6/?utm_source=share&utm_medium=web2x&context=3) on this [Reddit post showcasing kui.nvim](https://new.reddit.com/r/neovim/comments/110znd4/kuinvim_an_experiment_into_a_real_graphical/) discussing the benefits of a terminal are that it's not a GUI. But if you were to use this, then how much would it be different from just using Obsidian with its various plugins along with with [Obisidian-bridge.nvim](https://github.com/oflisback/obsidian-bridge.nvim)?

So what makes a terminal a terminal, different from GUIs and full desktop environments? Is it the low resource usage, is it still low with Kitty Graphics and kui.nvim? Is it the keyboard-centric interaction for higher efficiency? Is it because of the other benefits of commands environments, like unix stdin and stdout piping? If you want full blown GUIs in a terminal environment then how is it much different than using a GUI app with full keyboard navigation and text inputs? How do you feel about rendering full GUI graphics in a terminal?

Personally I like the idea of rendering graphics in a terminal environment is it would be overall better than using GUI apps for the reasons listed above, but I'm feeling reluctant on that.