A "degenerate special case" of a general concept, in mathematics [1], is a special case that no longer has the complexities that motivated the need for that concept in the first place.
Consider, for example, the evolution of a CRUD app that was first written in, say, the late 80s for OS/400, using an interaction style where it's all full screen forms rendered as text that you fill out with your keyboard, then submit. Say, you rewrote that app in the 00s in Windows Forms but using the same interaction design, and then again in the 20s as a browser-based app. If you look at the evolution of what happened to UI technology through the lens of that app, you won't feel like anything is amiss in 2023, but you're also kind of missing the point of having a GUI in the first place, as opposed to, say, a text terminal.
Whenever I hear "all I need is a textedit and a button" from a web developer, I kind of assume that this is what informs their viewpoint.
If you instead look at the evolution of UI technology through the lens of an app like Photoshop, it will immediately be obvious to you what it is that GUIs uniquely have to offer that, for example, text terminals can't, and why rewriting such a UI in a browser is anything but trivial.
[1] https://en.wikipedia.org/wiki/Degeneracy_(mathematics)