I got the notification to the announcement because I'm tracking the Categories:
Those two green boxes under the title can be used to verify... just click on each and then click the Bell to the far right. Select Tracking, the bell icon will go green.
My recommendation is to set the category to "watching." There are no posts other than release notes in this category, so every notification is a post for a new release notes update.
The way you are showing it, you'd have to set each thread to "watching," so you couldn't have set 2.3.2 to watching three years ago, because the post has only been out for a few weeks.
If you set the subcategory to "Watching" as @neonturbo is showing above (which you likely have already done ), then you don't need to mark individual threads when a new update is released.