There is a specific plugin that would handle this situation:
https://github.com/discourse/discourse-moderator-attention
I believe it works like this:
Modifications / new posts on the end bump the visibility of the topic in the topic list and once a moderator has read the post it would return to it’s original position and no longer be highlighted for moderators.
Regardless of me perhaps being incorrect about the movement in position at least it’s highlighted with an asterisk for moderators.
Official description:
Discourse Moderator Attention
This plugin was designed for heavily moderated sites, once installed we track which moderator read which post and when.
Any unmoderated topics (topics with at least 1 unmoderated post) will be displayed in the topic list with and asterisk for moderators only.