The trick is to make it clear and descriptive enough without taking up much screen space.
The only thing I don't like about the idea of manually toggling it on
Possibility:
Every threat defaults to "tagged" and appears on screen.
Each threat can be "dismissed" individually if it is of limited/no concern to the player.
The potential for clutter is high though, so maybe only the first x most imminent threats are displayed, and when they either expire or are dismissed the next one immediately takes its place if there are more than x active threats.
What is x though?
I'm running with screen height of 1080, and could proabably fit 5 or 6 events fairly comfortably under the date counter.
Not everyone will have the same settings or preferences, so it might be an idea to limit x to 3 or 4 for maximum compatibility with the widest range of possible display configs, and then add a line in settings.json so the player can adjust this if desired.
But just having the 3 most imminent active threats on display would still be incredibly useful.