I don’t think there is anything default available for this, but maybe it can be done with
They have this trigger
Which maybe you can re-use in a custom script in combination with a filter such as unsolved?
Worth looking into imo, but will take some dev work probably.
Simpler approach might be looking at auto-bump settings:
It’s not exactly what you want, but you could make open topics in a certain category bump daily, to draw attention. As long as you’re diligent with closing them when resolved (or setting an auto-close), that might work.
But if you want it specifically for moderators, and specifically a notification, I think the automation plugin is your best bet atm.