Looks like the Rarity entry in Blizzard's UI is no longer added immediately, meaning /rarity must first be used to load the addon. This might be a side effect of moving to the new LoadOnDemand system (see #752).

Should be easy to fix, but I haven't looked into it yet.

Correct. Using the minimap button to open the settings also works.

Right. I guess it would be a little unfortunate to leave this unresolved, but I don't see a way of adding the category without loading the Options module (separate addon) at a glance. It might be possible to create a "placeholder" category with a button that says "Load Options module", as some other addons do. That would certainly take some work to implement and test, though.

Since I'm out of time, I'll create a tagged release anyway and hope there won't be too many bug reports 🤷‍♂️