Thanks, but it doesn't appear to. It's largely unchanged from earlier versions (dating back many years).

Unbelievable. How do you ruin such an essential part of a product with such a stupid regression?

Can you access the Styles Pane? (not the drop down?)
Here are Styles Panes from two Windows versions. Note controls at the bottom.
00 deleteme 1.png00 deleteme 2.png

In Word 2003, when I change the styles displayed in the Styles Pane to "All Styles" in the Drop Down I get something like what you are seeing. That is, these options for the Styles Pane change not just that pane's display but other displays of styles as well.
00 deleteme 3.png
I can do the same thing through the Styles Pane in later versions as well.

You just noticed this? 2011 is an old product, I believe it is out of support by MS. I assume you've had it for a while and this just happened. I do not think MS has made any changes to Word 2011 in the last couple of years.

I've used Word since Word 3 on the Mac and including Windows versions Word 97, 2000, 2002, 2003, 2007, 2010, 2013 and 2016. To the best of my recollection, in all of those, there has been a control available to change which styles are displayed. I suspect you are missing it.