If you look at how Python is used in 3D graphics (or similar DSLs in the more esoteric 3D apps), they've been using the scripting system in the likes of Maya and Blender to create inordinately complicated systems for decades. Like 3D graphics, a lot of UI code is visual, ephemeral, complex. The development process for such features, benefits from from the speed of iteration and flexibility that dynamically typed code can provide.

Granted, a checkout, or a clinical case management form (for example) will definitely benefit from the kind of precision a strong type system will encourage.

Beyond that, we should think more about the how and why, because type wrangling can slow down delivery, experimentation, and cannot guarantee the prevention of bugs.

Gmail and Google Maps for example, at least when those projects started out, had no TypeScript in their UI code.

Google Maps, even in it's earliest iteration, far outstrips the complexity of most TypeScript applications in the wild today. And also has a greater requirement for precision than many of the applications that we can call to mind, outside of Finance, Transport, Construction, or Medicine.

People seem to talk as though certain applications were impossible to build without without TypeScript, but that is simply not true.

So TLDR, answering the root of your question, TS is not at all necessary. But it can be helpful. Yet we're in a position now where it's almost intractable, and I don't think that's an ideal situation.