When is the nano-texture glass Pro Display XDR better than the standard one? I've seen both the glossy and the nano-texture version of Apple Pro Display XDR in real life, and the image quality of both is stunning.

I did notice that while the glossy version reflected the bright lights in the Apple store, you could see hardly any glare on the nano-texture version of the display. However, the text displayed on the nano-texture version was perhaps a tiny bit less crisp and the colours were not as vivid as on the standard glass version (I did look really close, though, which I wouldn't do under normal circumstances).

So I wonder, except for the obvious case where one works in an environment where there's plenty of bright lights, are there any other contexts where the nano-texture is better suited than the standard glass? I.e. video editing, working with text, photography, etc.

Or is it simply the question of personal preference and whether someone likes to see their reflection in the screen or not?

In your answers, please assume that while I have plenty of experience using Apple displays to work with text/code, I have only beginner-level knowledge of video and photo editing, so any observations you share are valuable.
You kinda got it all... that's it. It's just an improved matte display that minimizes reflections and glare, at the cost of some saturation and crispness. The only difference is how the matte effect is done: in a standard matte display, it's a coating, while on the Pro Display XDR, it's etched into the glass.

In a professional environment, the requirements are really the same as a non-professional one: while the glossy version is better if you can work in a controlled lighting environment, that privilege isn't always available (such as on-location shoots), and the benefits of the matte display can outweigh the downsides. It really does just depend on preference and working environment.