It looks like there is a small bug or limitation, I’m not sure if it’s new since this component was ported to Glimmer, because previously I was using a different component for this functionality.
The problem is that when an ignored user posts in a watched/tracked topic it still shows the (1) for new posts next to its title in the topic list. And since the the post is hidden from the user, even after clicking into the topic and scrolling all the way to the bottom it still shows the new post notification in the topic list. I assume it’s because the new post is invisible and therefore doesn’t get marked as read.